MEET:
Aidan O’Neill KC (Scot) KC
“By far, Aidan is the leading public law KC at the Scottish Bar. He generates incredibly high-quality work."
Chambers & Partners, 2025
Silk (Scot): 1999
Called to the Scottish Bar in 1987, to the Bar of England and Wales in 1996 and to the Irish Bar in Dublin in December 2020, Aidan was appointed Queen’s (now King’s) Counsel in Scotland in 1999, and became Queen’s (now King’s) Counsel in England and Wales in 2017. He is therefore a “double silk”, one of only a handful in the UK. He enjoys wide ranging litigation and legal advisory practice across the UK (including court appearance in Northern Ireland).
He has particular experience and expertise in competition law, in commercial and constitutional judicial review, in environmental/Aarhus law and in employment/equality law. He is a specialist in EU law, in human rights law and in UK constitutional law.
He is a highly experienced pleader before the top courts, being among the top ten barristers across the UK – as ranked in terms of the number of appearances as leading counsel – in cases before the UK Supreme Court (UKSC) in its first decade of operations since its establishment in October 2009. He has appeared on a number of occasions before the Court of Justice of the European Union (CJEU) in Luxembourg, both before and (by virtue of his membership of the Irish Bar) since Brexit. He has also appeared before the European Court of Human Rights in Strasbourg.
UKHL/UKSC/JCPC
1. Daly v. His Majesty’s Advocate [2025] UKSC 38: on the ECHR/HRA 1998 compatibility of the restrictions placed – whether at common law or under reference to the “rape shield provisions” contained in sections 274 to 275B of the Criminal Procedure (Scotland) Act 1995 – on the admissibility, in criminal trials for serious sexual offences, of evidence concerning complainants’ sexual history. Written and oral submissions on behalf of the appellant, Daly.
2. For Women Scotland Ltd v Scottish Ministers [2025] UKSC 16: the UKSC reversed the decisions of the courts below ([2023] CSIH 37, [2022] CSOH 90) and found that the statutory guidance promulgated by the Scottish Ministers under Section 7 of the Gender Representation on Public Boards (Scotland) Act 2018 concerning the definition of “woman” in the Equality Act 2010 was incorrect. A person with a gender recognition certificate (GRC) in the female gender did not come within the definition of “woman” for the purposes of sex discrimination in section11 of the 2010 Act. Accordingly, the definition of “woman” in section 2 of the 2018 Act – which the Scottish Ministers accepted had to bear the same meaning as the term “woman” in sections 11 and 212 of the 2010 Act – was limited to biological women regardless of whether or not they held a GRC but did not include trans identifying men holding a GRC. Written and oral submissions on behalf of the appellants, For Women Scotland.
3. Jersey Choice Ltd v HM Treasury [2024] UKSC 5; [2021] EWCA Civ 1941; [2020] EWHC 3258 (Ch): on whether the removal by the UK of VAT relief from low value goods sold to UK customers using mail order from the Channel Islands was in breach of EU law sufficient to found a claim in Francovich damages against the UK. Written and oral submissions on behalf of the appellant, Jersey Choice Ltd.
4. Craig (James) v HM Advocate [2022] UKSC 6; [2020] HCJAC 22: on whether a UK national’s extradition to the United States would be ultra vires because sought at a time when the “forum bar” provisions passed by the UK Parliament had unlawfully not been brought into force in Scotland, contrary to the decision in Craig v Advocate General [2018] CSOH 117 2019 SC 230. Written and oral submissions on behalf of the appellant, James Craig.
5. Anwar v. Secretary of State for Business, Energy and Industrial Strategy [2021] UKSC 44; [2019] CSIH 43: whether or not a failure by the UK to make express statutory provision to allow for employment tribunals to pronounce protective freezing orders against respondents in discrimination cases pending before them constituted a breach of the UK’s obligation under EU law to provide for remedies sufficient to ensure effective legal protection in the fields covered by EU law such as to found a claim in Francovich damages. Written and oral submissions on behalf of the appellant, Anwar.
6. Cherry v. Advocate General for Scotland/Miller v. Prime Minister [2019] UKSC 41; [2019] CSIH 49; [2019] CSOH 70: JR as to the lawfulness/constitutionality of the Crown’s (on the advice of the Prime Minister) prorogation of Parliament on 28 August 2019. Written and oral submissions on behalf of the Cherry appellants.
7. Maguire’s Judicial Review of the General Council of Bar of Northern Ireland [2018] UKSC 17; [2015] NIQB 4: JR of the compatibility of NI Bar Council rules requiring instruction of senior counsel with Convention right to lawyer of one’s choosing. Written and oral submissions on behalf of the appellant, Maguire.
8. SM (Algeria) v. Entry Clearance Office, UK Visa Section [2018] UKSC 9: on whether family member for purposes of EU free movement includes child under Islamic kefalah. Written and oral submissions on behalf of the intervener, the AIRE Centre.
9. Scotch Whisky Association v. Scottish Ministers [2017] UKSC 76; [2016] CSIH 77; EU:C:2015:845; [2014] CSIH 38; [2013] CSOH 70: JR re the compatibility minimum pricing for alcohol with EU free movement of goods/Common Agricultural Policy. Written and oral submissions on behalf of the Scotch Whisky Association appellants.
10. Janah v. Libya/Benkharbouche v. Sudan [2017] UKSC 62; [2015] EWCA Civ 33: on whether EU law principles of access to court may disapply State immunity claims in ET applications. Written and oral submissions on behalf of the intervener, the AIRE Centre.
11. R (UNISON) v. Lord Chancellor [2017] UKSC 51: JR on the incompatibility with fundamental right of access to the court of fees imposed by the executive on use of Employment Tribunals. Written submissions on behalf of the intervener, the Independent Workers Union of Great Britain.
12. AB v. Her Majesty’s Advocate [2017] UKSC 25; [2017] HCJAC 70: criminal appeal challenge to the lawfulness of removal of reasonable belief defence as to the age of a sexual partner. Written and oral submissions on behalf of the appellant, AB.
13. R (Miller) v Secretary of State [2017] UKSC 5: JR on whether the executive could, without specific statutory authorisation, trigger the Article 50 TEU process for the UK to leave the EU. Written submissions on behalf of the intervener, the Independent Workers Union of Great Britain.
14. R (Shindler) v. Chancellor of the Duchy of Lancaster 24 May [2016] UKSC 2016/0105; [2016] EWCA Civ 469; [2016] EWHC (Admin) 957: JR challenge to the EU and common law constitutional compatibility of the exclusion from the Brexit referendum franchise of British citizens who had exercised their EU free movement and citizenship rights to live elsewhere in the EU outside the UK for more than 15 years. Written and oral submissions for permission to appeal on behalf of the Shindler appellants.
15. Christian Institute and others v. Lord Advocate [2016] UKSC 61; [2015] CSIH 64; [2015] CSOH 7: JR on Data Protection grounds of the “named person service” provisions in Part 4 of the Children and Young People (Scotland) Act 2014. Written and oral submissions on behalf of the Christian Institute appellants.
16. Hainsworth v. Ministry of Defence [2015] UKSC (1 December 2015): re Article 5 of Directive 2000/78 and the duty of an employer to make reasonable adjustments within the context of associative discrimination to accommodate the disability needs of a dependent child of an employee. Written and oral submissions for permission to appeal on behalf of the intervener, the Equality and Human Rights Commission (EHRC).
17. Moohan and others v. Scottish Government [2014] UKSC 67; [2014] CSIH 56; [2014] CSOH 199: JR of the Scottish Independence Referendum (Franchise) Act 2013 for its exclusion of convicted prisoners from its franchise. Written and oral submissions on behalf of the Moohan appellants.
18. R (Sandiford) v. Foreign and Commonwealth Office [2014] UKSC 44; [2013] EWCA Civ 581; [2013] EWHC 168 (Admin): on whether the FCO had duties at common law under the ECHR to provide funding for legal representation of British nationals facing death penalty abroad. Written and oral submissions on behalf of the Sandiford appellant.
19. Bull v. Preddy and Hall [2013] UKSC 73: whether Christian guest house owners could, on grounds of religious conviction, lawfully refuse a double-bedded room to a same sex couple in a civil partnership. Written and oral submissions on behalf of the appellants, Mr. and Mrs. Bull.
20. R. (Chester) v Secretary of State for Justice/McGeoch v. Lord President of the Council [2013] UKSC 63; [2011] CSIH 67; [2011] CSOH 65: JR of prisoners’ disenfranchisement from elections following within ambit of EU law, viz. local government and for European Parliament. Written and oral submissions on behalf of the McGeoch appellant.
21. Walton (formerly Roadsense) v. Scottish Ministers [2012] UKSC 44; [2011] CSOH 131: EU law and the Aarhus Convention challenge in context of statutory planning appeal in relation to duties of strategic environmental assessment, public consultation and statutory title of “persons aggrieved” to object to road schemes on environmental grounds. Written and oral submissions on behalf of the Walton appellant.
22. Ravat v. Halliburton Manufacturing & Services Ltd. [2012] UKSC 1; [2010] CSIH 52: whether a UK employment tribunal had jurisdiction to adjudicate on an unfair dismissal claim from an oil industry employee working outside the EU for a German company. Written and oral submissions on behalf of the Ravat appellant.
23. AXA General Insurance v. Lord Advocate [2011] UKSC 46; [2011] CSIH 31; [2010] CSOH 2: judicial review of the validity and Convention compatibility of the Damages (Asbestos-related conditions) (Scotland) Act 2009. Written and oral submissions on behalf of the third to tenth respondents, all individual sufferers from asbestos-related conditions.
24. R. (Cart) v Upper Tribunal [2011] UKSC 28/Eba v. Advocate General for Scotland [2011] UKSC 29 – on the susceptibility of decisions of the Upper Tribunal to judicial review in Scotland and England and Wales. Written submissions on behalf of the intervener, JUSTICE.
25. Cadder v. Her Majesty’s Advocate [2010] UKSC 43: criminal appeal challenge on the Convention right to have a solicitor present during a police interview while in police detention. Written and oral submissions on behalf of the intervener, JUSTICE.
26. R (JF and Thompson) v. Minister of Justice [2010] UKSC 17: JR on Article 8 ECHR right to privacy and its compatibility with the imposition of indefinite period of notification on the sex offenders’ register without provision for review or removal. Written and oral submissions on behalf of the intervener, A petitioner.
27. Somerville v Scottish Ministers [2007] UKHL 44, where the UKHL reversed the decisions of the courts below ([2006] CSIH 62) and held that a claim for damages as just satisfaction in respect of an act by a member of the Scottish Executive which was outside devolved competence because it was incompatible with a Convention right could be brought directly under the Scotland Act 1998 and was not subject to the time bar and limitation provisions contained in Section 7(5) of the Human Rights Act 1998. Written and oral submissions on behalf of the Somerville appellants.
28. Beggs v Scottish Ministers [2007] UKHL 3 holding that the First Division of the Inner House of the Court of Session had erred in law in [2006] CSIH 34 pronouncing an order requiring the attendance of two senior civil servants at a hearing to determine whether the Scottish Ministers had breached an undertaking so as to place them in contempt of court. The judges had acted inappropriately in failing to discuss their proposed course of action with counsel for the ministers, in failing to explain to the civil servants why their attendance was required and in failing to warn them of what might happen at the hearing. Written and oral submissions on behalf of the Beggs respondent.
29. Davidson v Scottish Ministers (No.1) [2005] UKHL 74 reversing the court below ([2021] CSIH, 18 Dec 2001 reported as 2002 SC 205) and holding that the proviso in Section 21(1)(a) the Crown Proceedings Act 1947 limiting available remedies against the Crown applied only in proceedings against the Crown to enforce a pursuer or claimant’s private law rights. Accordingly the courts could grant an interim or final interdict or an interim or final order for specific performance in public law proceedings against the Crown. Written and oral submissions on behalf of the Davidson appellant.
30. Davidson v Scottish Ministers (No.2) [2004] UKHL 34; upholding the decision of the Second Division ([2002] CSIH, 11 September 2002) in holding that where a government minister who had drafted or promoted legislation subsequently became a judge, and was required to give a judicial ruling upon the effect of that legislation, there was a real risk of apparent bias. This is because, despite the judicial oath, there was a very real possibility that that the judge would subconsciously strive to avoid reaching a conclusion that would undermine the assurances he had previously given to Parliament. Written and oral submissions on behalf of the Davidson respondent.
31. Archibald v. Fife Council [2004] UKHL 32 on appeal from an Extra Division of the Inner House ([2003] CSIH, 9 December 2003, reported as 2004 SC 495) concerning the scope of the duty of reasonable adjustment under sections 5 and 6 of the Disability Discrimination Act 1995. Written and oral submissions on behalf of the Fife Council respondent.
32. Davidson v Scottish Ministers (No. 3) (Incidental Petition: Dismissal of Appeal) [2005] UKHL, 31 Jul 2003 and reported as 2005 1 SC (HL) 1) holding that while leave of the Inner House to appeal to the UKHL was required on an appeal against an interlocutory judgment, no such permission was required in respect of an appeal following a substantive decision. A substantive decision was one that was substantive in form, not just in name, and where a whole issue had been disposed of. The Scottish Ministers were therefore entitled to appeal against the decision of the Second Division below [2002] CSIH, 11 September 2002 and reported as 2003 SC 103) without having sought or obtained leave from the Inner House. Written and oral submissions on behalf of the Davidson respondent.
33. MacDonald v Ministry of Defence [2003] UKHL 34 where the House of Lords held – upholding the 2:1 majority decision of the Inner House (2002 SC 1, [2002] ICR 174) to reverse the decision of the EAT ([2001] ICR 1) which had itself overturned the decision of the Employment Tribunal – that he Sex Discrimination Act 1975 does not cover discrimination on the ground of sexual orientation. Thus, where a gay man who was dismissed by RAF on ground of his sexuality the proper comparator in any claim to sex discrimination was a person of opposite sex who was also homosexual. Since a lesbian servicewoman would have been similarly treated by being summarily dismissed by the RAF, he could not complaint of unlawful discrimination under the law as it then stood. Written and oral submissions on behalf of the MacDonald appellant.
34. Millar v Dickson [2001] UKPC D 4 where the Judicial Committee of the Privy Council exercising its then devolution jurisdiction overturned the decision of the High Court of Justiciary Appeal Court ([2000 HCJAC, 3 August 2000 reported as 2000 JC 648) to hold that a prosecution conducted before a temporary sheriff constituted a breach of the defendant’s right to be tried before an independent and impartial tribunal compatibly with Article 6 ECHR. Written and oral submissions on behalf of the Dickson appellant.
35. Litster v. Forth Dry Dock Engineering Co. Ltd., (UKHL 16 March 1989( 1989 SC (HL) 96, [1990] 1 AC 546, HL – on the proper approach to the interpretation and application of the Transfer of Undertakings (“TUPE”) Regulations in the light of EU law. Appearing as junior counsel on behalf of the Litster appellant
Court of Justice of the European Union
1. Joined Case C-428/24 and C-476/24 FZ AR : re the freezing of assets held in a trust EU:C:2026:408 CJEU reference from the Lazio Administrative Court, Italy on whether the EU sanctions regime extended to the freezing of assets held in trust. Written and oral submissions on behalf of the intervener, EuroChem AG.
2. Case C-93/18 Bajratari v. Secretary of State for the Home Department EU:C:2019:512 – CJEU reference from the Court of Appeal of Northern Ireland (“NICA”) on whether income from employment deemed “unlawful” under UK law may establish, in whole or in part, the availability of sufficient resources for EU law purposes under Article 7(1)(b) of the Citizens Directive. Written and oral submissions on behalf of the intervener, the AIRE Centre
3. Case C-129/18 SM (Algeria) v. Entry Clearance Office, UK Visa Section EU:C:2019:248 – CJEU reference from the UKSC on whether family member for purposes of EU free movement includes child adopted/fostered under Islamic Sharia law kefalah. Written and oral submissions on behalf of the intervener, the AIRE Centre
4. Case C-621/18 Wightman v. Secretary of State for Exiting the European Union EU:C:2018:999; [2018] CSIH 62; [2018] CSOH 61; [2018] CSIH 18; [2018] CSOH 8 – CJEU reference from the CSIH on whether the UK’s notification of intention to leave the EU under Article 50 TEU was unilaterally revocable by the UK during the notice period set out in the Treaty. Written and oral submissions on behalf of the Wightman petitioners.
5. Case C-333/14 Scotch Whisky Association and others v. Scottish Ministers EU:C:2015:845 – CJEU reference from the CSIH re compatibility of minimum pricing for alcohol with the principle of the EU free movement of goods/Common Agricultural Policy. Written and oral submissions on behalf of the Scotch Whisky Association petitioners
6. Case C-20/00 Booker Aquaculture (t/a Marine Harvest McConnell) v. Scottish Ministers EU:C:2003:397 – CJEU reference from the CSIH on whether there was an EU law right to compensation in respect of losses arising from public health/disease control measures. Written and oral submissions on behalf of the Booker Aquaculture petitioners.
Dec 2023 – Aug 2026 Honorary Professor, University of St Andrews and the School of History’s Institute of Legal and Constitutional Research.
2016-2022 Equality and Human Rights Commission “A” Panel (both Scotland and England & Wales) of senior counsel
2017 Fee paid (part-time) Chair of the First Tier Tribunal for Scotland – Housing and Property Chamber
2015 Fee paid (part-time) Chair of the First Tier Tribunal of the Scottish Tax Tribunal
2009-2013 Chairman of the Edinburgh Centre for Constitutional Law and Honorary Fellow in the School of Law, University of Edinburgh
2008 and 2009 Teaching Fellow in the Law and Public Affairs Program at Princeton University, NJ, USA.
Aidan is the author of a substantial number of academic articles, blog posts and legal practitioner texts including EU law for UK Lawyers (soon to be updated to EU law after Brexit: a guide for the perplexed), and he regularly presents papers at legal conferences and seminars.
Aidan holds the undergraduate degree of LL.B (First Class Hons.) from Edinburgh Law School as well as an LL.M. (First Clas Hons) from the University of Sydney Australia, and an LL.M in International and European law from the European University Institute, Florence. In 2012 he was awarded a doctorate (LL.D.) by the University of Edinburgh on the basis that his publication record was adjudged by an academic panel to have made a substantial and significant contribution to legal scholarship.
Aidan is committed to protecting and respecting your privacy. In order to provide legal services to their clients, including advice and representation services, Aidan needs to collect and hold personal data. This includes their client’s personal data and the personal data of others who feature in the matter upon which they are instructed. To read Aidan’s privacy notice in full, please see here.
“Aidan is a brilliant advocate who commands respect in the courtroom.”
He is “a silk who possesses an extraordinary breadth and depth of knowledge.”
Chambers & Partners and Legal 500, 2024
See further:
https://chambers.com/lawyer/aidan-oneill-kc-uk-bar-14:224963
https://www.legal500.com/c/scottish-bar/administrative-and-public-law/silks
https://www.legal500.com/c/scottish-bar/employment/silks
"Aidan is rightly seen as one of the leading silks at the Scottish Bar."
"Aidan O'Neill is one of the very best KCs in terms of commitment and knowledge." "Aidan has a brilliant ability to find a way through even the most complicated legal issues."
"Aidan O'Neill KC is involved in cases of the most profound constitutional significance, appearing before the highest courts in the UK and EU. He specialises in challenges against government policy on public law, human rights or EU law grounds. He is renowned for his willingness to argue difficult cases, predominantly on behalf of petitioners." "Aidan has extraordinarily knowledge of the law which cannot be surpassed by anybody and the ability to find issues in a very creative and thoughtful way. His advocacy is robust and respectful."
"Dual-qualified in Scotland and England, Aidan O'Neill KC possesses experience in important cases on Brexit, employment rights, free movement for EU citizens and the prohibition on trade restrictions between EU member states."
"Aidan O'Neill KC is a walking encyclopedia when it comes to EU law." "Aidan O'Neill KC's knowledge and expertise in Scottish and European law is unparalleled."
"Phenomenal knowledge of all areas with what must be a photographic memory for law, and indeed outside law so that external issues can be brought to bear in legal arguments. A simply extraordinary talent."
"A silk who possesses an extraordinary breadth and depth of knowledge."
"Aidan is a brilliant advocate who commands respect in the courtroom." "Aidan is absolutely the top of his game and the go-to person for a judicial review. His technical knowledge is outstanding and he is also very commercial. He has excellent client care skills too."
"Aidan is a tour de force on his feet. He thinks very quickly and is able to pull together lateral arguments beautifully."
"A huge intellect with a huge capacity for work. If you are looking for counsel who will give it their all, that is Aidan O'Neill KC."
"Aidan is a standout for his human rights work. He has an encyclopedic brain, he is hugely industrious and he is also very user-friendly. His court manner is forceful and robust." "He is a hugely experienced silk. He is very knowledgeable and is really great to work with."
"He is a very tenacious and fearless oral advocate." "He has a phenomenal intellect but is down to earth and easy to work with."
"His forte is in debating the court - he is never satisfied with the final version of an argument and is always looking to improve it."
"Obviously highly regarded, he does a lot of very high-profile cases and is very fiery and passionate."
"Unparalleled knowledge of the area and utter commitment to the piece of work being carried out. The best QC in this field given the breadth and depth of knowledge."
"A very excellent court performer who is good on his feet; he is passionate about the cases he takes on. The fact that he is also qualified in Scotland is a particular bonus for us in that it gives him a good perspective compared to others." "His breadth and depth and knowledge are breathtaking; he surprises me with bits of information all the time."
"Aidan O'Neill QC is demanding and exacting, but what he produces is extraordinary." "He gets a fantastic range of interesting work."
"His breadth and depth is amazing." "He is excellent on his feet, and comes up with very interesting and creative arguments." Chambers & Partners also states that "Aidan is very well known, is excellent on his feet and comes with very interesting and creative arguments." "He is very good on his feet, robust and confident in his position without being bullish."
"His breadth and depth of knowledge both in the law in English law, Scottish law and European law as well as international law is simply mind boggling."
"Extremely user-friendly and supremely swift at getting to the heart of matters." "Experienced and capable of putting together ground-breaking arguments as well as incredibly approachable and helpful." Chambers & Partners also notes that Aidan "has terrific judgement and is very good at reading a court." "The depth and breadth of his legal knowledge is incredible."
"Has phenomenal knowledge of the law."
"His main strength is his ability to consider work or areas of law at short notice and be familiar with them quickly."
"Someone to go to if you have a difficult claimant-side case and want to fight really hard."
"Very helpful and focused. Pays great attention to detail."
"Very knowledgeable and practical in relation to proceedings with a Scottish dimension, and an expert on EU law.” “His written advocacy is excellent. He’s an utterly comprehensive and knowledgeable advocate with virtually unrivalled experience in the higher courts."
"A natural, enthusiastic orator, whose breadth of practice is staggering."
"Knows more about European Law than anyone else and he is incredibly creative with his ideas”. “A heavy hitter, he produces spectacular written notes that show his learning and he is never second bested on them."
"The Supreme Court is his natural forum – he can more than hold his own in that environment and is clearly well-respected there.” “His advocacy skills are tremendous, he is intellectually impressive and he is prepared to take on extremely difficult and notorious work."
"He has an excellent grasp of cutting-edge issues” and “The other side are always extremely intimidated by his knowledge of the law."
MAIN AREAS OF PRACTICE:
- Civil Liberties and Human Rights
- Commercial Law
- Commercial Public Law
- Competition and EU
- Crime
- EU Law
- Election Law
- Employment Law
- Environmental Law and Natural Resources
- Equality and Discrimination Law
- International Arbitration
- International Law
- Mediation
- Police, Inquests and Prison
- Public Law
- Regulatory Offences
+44 (0)20 7404 3447
Silk (Scot): 1999
“By far, Aidan is the leading public law KC at the Scottish Bar. He generates incredibly high-quality work."
Chambers & Partners, 2025
MAIN AREAS OF PRACTICE
- Commercial Law
- Election Law
- Employment Law
- Civil Liberties and Human Rights
- Public Law
- Police, Inquests and Prison
- Commercial Public Law
- Equality and Discrimination Law
- Competition and EU
- Crime
- Regulatory Offences
- EU Law
- International Law
- Environmental Law and Natural Resources
- Mediation
- International Arbitration
Aidan O’Neill KC (Scot) KC
Contact Aidan: aidanoneill@matrixlaw.co.uk | +44 (0)20 7404 3447
Contact Aidan's Practice Team (Team M): TeamM@matrixlaw.co.uk
Called to the Scottish Bar in 1987, to the Bar of England and Wales in 1996 and to the Irish Bar in Dublin in December 2020, Aidan was appointed Queen’s (now King’s) Counsel in Scotland in 1999, and became Queen’s (now King’s) Counsel in England and Wales in 2017. He is therefore a “double silk”, one of only a handful in the UK. He enjoys wide ranging litigation and legal advisory practice across the UK (including court appearance in Northern Ireland).
He has particular experience and expertise in competition law, in commercial and constitutional judicial review, in environmental/Aarhus law and in employment/equality law. He is a specialist in EU law, in human rights law and in UK constitutional law.
He is a highly experienced pleader before the top courts, being among the top ten barristers across the UK – as ranked in terms of the number of appearances as leading counsel – in cases before the UK Supreme Court (UKSC) in its first decade of operations since its establishment in October 2009. He has appeared on a number of occasions before the Court of Justice of the European Union (CJEU) in Luxembourg, both before and (by virtue of his membership of the Irish Bar) since Brexit. He has also appeared before the European Court of Human Rights in Strasbourg.
Selection of Past Court Cases
UKHL/UKSC/JCPC
1. Daly v. His Majesty’s Advocate [2025] UKSC 38: on the ECHR/HRA 1998 compatibility of the restrictions placed – whether at common law or under reference to the “rape shield provisions” contained in sections 274 to 275B of the Criminal Procedure (Scotland) Act 1995 – on the admissibility, in criminal trials for serious sexual offences, of evidence concerning complainants’ sexual history. Written and oral submissions on behalf of the appellant, Daly.
2. For Women Scotland Ltd v Scottish Ministers [2025] UKSC 16: the UKSC reversed the decisions of the courts below ([2023] CSIH 37, [2022] CSOH 90) and found that the statutory guidance promulgated by the Scottish Ministers under Section 7 of the Gender Representation on Public Boards (Scotland) Act 2018 concerning the definition of “woman” in the Equality Act 2010 was incorrect. A person with a gender recognition certificate (GRC) in the female gender did not come within the definition of “woman” for the purposes of sex discrimination in section11 of the 2010 Act. Accordingly, the definition of “woman” in section 2 of the 2018 Act – which the Scottish Ministers accepted had to bear the same meaning as the term “woman” in sections 11 and 212 of the 2010 Act – was limited to biological women regardless of whether or not they held a GRC but did not include trans identifying men holding a GRC. Written and oral submissions on behalf of the appellants, For Women Scotland.
3. Jersey Choice Ltd v HM Treasury [2024] UKSC 5; [2021] EWCA Civ 1941; [2020] EWHC 3258 (Ch): on whether the removal by the UK of VAT relief from low value goods sold to UK customers using mail order from the Channel Islands was in breach of EU law sufficient to found a claim in Francovich damages against the UK. Written and oral submissions on behalf of the appellant, Jersey Choice Ltd.
4. Craig (James) v HM Advocate [2022] UKSC 6; [2020] HCJAC 22: on whether a UK national’s extradition to the United States would be ultra vires because sought at a time when the “forum bar” provisions passed by the UK Parliament had unlawfully not been brought into force in Scotland, contrary to the decision in Craig v Advocate General [2018] CSOH 117 2019 SC 230. Written and oral submissions on behalf of the appellant, James Craig.
5. Anwar v. Secretary of State for Business, Energy and Industrial Strategy [2021] UKSC 44; [2019] CSIH 43: whether or not a failure by the UK to make express statutory provision to allow for employment tribunals to pronounce protective freezing orders against respondents in discrimination cases pending before them constituted a breach of the UK’s obligation under EU law to provide for remedies sufficient to ensure effective legal protection in the fields covered by EU law such as to found a claim in Francovich damages. Written and oral submissions on behalf of the appellant, Anwar.
6. Cherry v. Advocate General for Scotland/Miller v. Prime Minister [2019] UKSC 41; [2019] CSIH 49; [2019] CSOH 70: JR as to the lawfulness/constitutionality of the Crown’s (on the advice of the Prime Minister) prorogation of Parliament on 28 August 2019. Written and oral submissions on behalf of the Cherry appellants.
7. Maguire’s Judicial Review of the General Council of Bar of Northern Ireland [2018] UKSC 17; [2015] NIQB 4: JR of the compatibility of NI Bar Council rules requiring instruction of senior counsel with Convention right to lawyer of one’s choosing. Written and oral submissions on behalf of the appellant, Maguire.
8. SM (Algeria) v. Entry Clearance Office, UK Visa Section [2018] UKSC 9: on whether family member for purposes of EU free movement includes child under Islamic kefalah. Written and oral submissions on behalf of the intervener, the AIRE Centre.
9. Scotch Whisky Association v. Scottish Ministers [2017] UKSC 76; [2016] CSIH 77; EU:C:2015:845; [2014] CSIH 38; [2013] CSOH 70: JR re the compatibility minimum pricing for alcohol with EU free movement of goods/Common Agricultural Policy. Written and oral submissions on behalf of the Scotch Whisky Association appellants.
10. Janah v. Libya/Benkharbouche v. Sudan [2017] UKSC 62; [2015] EWCA Civ 33: on whether EU law principles of access to court may disapply State immunity claims in ET applications. Written and oral submissions on behalf of the intervener, the AIRE Centre.
11. R (UNISON) v. Lord Chancellor [2017] UKSC 51: JR on the incompatibility with fundamental right of access to the court of fees imposed by the executive on use of Employment Tribunals. Written submissions on behalf of the intervener, the Independent Workers Union of Great Britain.
12. AB v. Her Majesty’s Advocate [2017] UKSC 25; [2017] HCJAC 70: criminal appeal challenge to the lawfulness of removal of reasonable belief defence as to the age of a sexual partner. Written and oral submissions on behalf of the appellant, AB.
13. R (Miller) v Secretary of State [2017] UKSC 5: JR on whether the executive could, without specific statutory authorisation, trigger the Article 50 TEU process for the UK to leave the EU. Written submissions on behalf of the intervener, the Independent Workers Union of Great Britain.
14. R (Shindler) v. Chancellor of the Duchy of Lancaster 24 May [2016] UKSC 2016/0105; [2016] EWCA Civ 469; [2016] EWHC (Admin) 957: JR challenge to the EU and common law constitutional compatibility of the exclusion from the Brexit referendum franchise of British citizens who had exercised their EU free movement and citizenship rights to live elsewhere in the EU outside the UK for more than 15 years. Written and oral submissions for permission to appeal on behalf of the Shindler appellants.
15. Christian Institute and others v. Lord Advocate [2016] UKSC 61; [2015] CSIH 64; [2015] CSOH 7: JR on Data Protection grounds of the “named person service” provisions in Part 4 of the Children and Young People (Scotland) Act 2014. Written and oral submissions on behalf of the Christian Institute appellants.
16. Hainsworth v. Ministry of Defence [2015] UKSC (1 December 2015): re Article 5 of Directive 2000/78 and the duty of an employer to make reasonable adjustments within the context of associative discrimination to accommodate the disability needs of a dependent child of an employee. Written and oral submissions for permission to appeal on behalf of the intervener, the Equality and Human Rights Commission (EHRC).
17. Moohan and others v. Scottish Government [2014] UKSC 67; [2014] CSIH 56; [2014] CSOH 199: JR of the Scottish Independence Referendum (Franchise) Act 2013 for its exclusion of convicted prisoners from its franchise. Written and oral submissions on behalf of the Moohan appellants.
18. R (Sandiford) v. Foreign and Commonwealth Office [2014] UKSC 44; [2013] EWCA Civ 581; [2013] EWHC 168 (Admin): on whether the FCO had duties at common law under the ECHR to provide funding for legal representation of British nationals facing death penalty abroad. Written and oral submissions on behalf of the Sandiford appellant.
19. Bull v. Preddy and Hall [2013] UKSC 73: whether Christian guest house owners could, on grounds of religious conviction, lawfully refuse a double-bedded room to a same sex couple in a civil partnership. Written and oral submissions on behalf of the appellants, Mr. and Mrs. Bull.
20. R. (Chester) v Secretary of State for Justice/McGeoch v. Lord President of the Council [2013] UKSC 63; [2011] CSIH 67; [2011] CSOH 65: JR of prisoners’ disenfranchisement from elections following within ambit of EU law, viz. local government and for European Parliament. Written and oral submissions on behalf of the McGeoch appellant.
21. Walton (formerly Roadsense) v. Scottish Ministers [2012] UKSC 44; [2011] CSOH 131: EU law and the Aarhus Convention challenge in context of statutory planning appeal in relation to duties of strategic environmental assessment, public consultation and statutory title of “persons aggrieved” to object to road schemes on environmental grounds. Written and oral submissions on behalf of the Walton appellant.
22. Ravat v. Halliburton Manufacturing & Services Ltd. [2012] UKSC 1; [2010] CSIH 52: whether a UK employment tribunal had jurisdiction to adjudicate on an unfair dismissal claim from an oil industry employee working outside the EU for a German company. Written and oral submissions on behalf of the Ravat appellant.
23. AXA General Insurance v. Lord Advocate [2011] UKSC 46; [2011] CSIH 31; [2010] CSOH 2: judicial review of the validity and Convention compatibility of the Damages (Asbestos-related conditions) (Scotland) Act 2009. Written and oral submissions on behalf of the third to tenth respondents, all individual sufferers from asbestos-related conditions.
24. R. (Cart) v Upper Tribunal [2011] UKSC 28/Eba v. Advocate General for Scotland [2011] UKSC 29 – on the susceptibility of decisions of the Upper Tribunal to judicial review in Scotland and England and Wales. Written submissions on behalf of the intervener, JUSTICE.
25. Cadder v. Her Majesty’s Advocate [2010] UKSC 43: criminal appeal challenge on the Convention right to have a solicitor present during a police interview while in police detention. Written and oral submissions on behalf of the intervener, JUSTICE.
26. R (JF and Thompson) v. Minister of Justice [2010] UKSC 17: JR on Article 8 ECHR right to privacy and its compatibility with the imposition of indefinite period of notification on the sex offenders’ register without provision for review or removal. Written and oral submissions on behalf of the intervener, A petitioner.
27. Somerville v Scottish Ministers [2007] UKHL 44, where the UKHL reversed the decisions of the courts below ([2006] CSIH 62) and held that a claim for damages as just satisfaction in respect of an act by a member of the Scottish Executive which was outside devolved competence because it was incompatible with a Convention right could be brought directly under the Scotland Act 1998 and was not subject to the time bar and limitation provisions contained in Section 7(5) of the Human Rights Act 1998. Written and oral submissions on behalf of the Somerville appellants.
28. Beggs v Scottish Ministers [2007] UKHL 3 holding that the First Division of the Inner House of the Court of Session had erred in law in [2006] CSIH 34 pronouncing an order requiring the attendance of two senior civil servants at a hearing to determine whether the Scottish Ministers had breached an undertaking so as to place them in contempt of court. The judges had acted inappropriately in failing to discuss their proposed course of action with counsel for the ministers, in failing to explain to the civil servants why their attendance was required and in failing to warn them of what might happen at the hearing. Written and oral submissions on behalf of the Beggs respondent.
29. Davidson v Scottish Ministers (No.1) [2005] UKHL 74 reversing the court below ([2021] CSIH, 18 Dec 2001 reported as 2002 SC 205) and holding that the proviso in Section 21(1)(a) the Crown Proceedings Act 1947 limiting available remedies against the Crown applied only in proceedings against the Crown to enforce a pursuer or claimant’s private law rights. Accordingly the courts could grant an interim or final interdict or an interim or final order for specific performance in public law proceedings against the Crown. Written and oral submissions on behalf of the Davidson appellant.
30. Davidson v Scottish Ministers (No.2) [2004] UKHL 34; upholding the decision of the Second Division ([2002] CSIH, 11 September 2002) in holding that where a government minister who had drafted or promoted legislation subsequently became a judge, and was required to give a judicial ruling upon the effect of that legislation, there was a real risk of apparent bias. This is because, despite the judicial oath, there was a very real possibility that that the judge would subconsciously strive to avoid reaching a conclusion that would undermine the assurances he had previously given to Parliament. Written and oral submissions on behalf of the Davidson respondent.
31. Archibald v. Fife Council [2004] UKHL 32 on appeal from an Extra Division of the Inner House ([2003] CSIH, 9 December 2003, reported as 2004 SC 495) concerning the scope of the duty of reasonable adjustment under sections 5 and 6 of the Disability Discrimination Act 1995. Written and oral submissions on behalf of the Fife Council respondent.
32. Davidson v Scottish Ministers (No. 3) (Incidental Petition: Dismissal of Appeal) [2005] UKHL, 31 Jul 2003 and reported as 2005 1 SC (HL) 1) holding that while leave of the Inner House to appeal to the UKHL was required on an appeal against an interlocutory judgment, no such permission was required in respect of an appeal following a substantive decision. A substantive decision was one that was substantive in form, not just in name, and where a whole issue had been disposed of. The Scottish Ministers were therefore entitled to appeal against the decision of the Second Division below [2002] CSIH, 11 September 2002 and reported as 2003 SC 103) without having sought or obtained leave from the Inner House. Written and oral submissions on behalf of the Davidson respondent.
33. MacDonald v Ministry of Defence [2003] UKHL 34 where the House of Lords held – upholding the 2:1 majority decision of the Inner House (2002 SC 1, [2002] ICR 174) to reverse the decision of the EAT ([2001] ICR 1) which had itself overturned the decision of the Employment Tribunal – that he Sex Discrimination Act 1975 does not cover discrimination on the ground of sexual orientation. Thus, where a gay man who was dismissed by RAF on ground of his sexuality the proper comparator in any claim to sex discrimination was a person of opposite sex who was also homosexual. Since a lesbian servicewoman would have been similarly treated by being summarily dismissed by the RAF, he could not complaint of unlawful discrimination under the law as it then stood. Written and oral submissions on behalf of the MacDonald appellant.
34. Millar v Dickson [2001] UKPC D 4 where the Judicial Committee of the Privy Council exercising its then devolution jurisdiction overturned the decision of the High Court of Justiciary Appeal Court ([2000 HCJAC, 3 August 2000 reported as 2000 JC 648) to hold that a prosecution conducted before a temporary sheriff constituted a breach of the defendant’s right to be tried before an independent and impartial tribunal compatibly with Article 6 ECHR. Written and oral submissions on behalf of the Dickson appellant.
35. Litster v. Forth Dry Dock Engineering Co. Ltd., (UKHL 16 March 1989( 1989 SC (HL) 96, [1990] 1 AC 546, HL – on the proper approach to the interpretation and application of the Transfer of Undertakings (“TUPE”) Regulations in the light of EU law. Appearing as junior counsel on behalf of the Litster appellant
Court of Justice of the European Union
1. Joined Case C-428/24 and C-476/24 FZ AR : re the freezing of assets held in a trust EU:C:2026:408 CJEU reference from the Lazio Administrative Court, Italy on whether the EU sanctions regime extended to the freezing of assets held in trust. Written and oral submissions on behalf of the intervener, EuroChem AG.
2. Case C-93/18 Bajratari v. Secretary of State for the Home Department EU:C:2019:512 – CJEU reference from the Court of Appeal of Northern Ireland (“NICA”) on whether income from employment deemed “unlawful” under UK law may establish, in whole or in part, the availability of sufficient resources for EU law purposes under Article 7(1)(b) of the Citizens Directive. Written and oral submissions on behalf of the intervener, the AIRE Centre
3. Case C-129/18 SM (Algeria) v. Entry Clearance Office, UK Visa Section EU:C:2019:248 – CJEU reference from the UKSC on whether family member for purposes of EU free movement includes child adopted/fostered under Islamic Sharia law kefalah. Written and oral submissions on behalf of the intervener, the AIRE Centre
4. Case C-621/18 Wightman v. Secretary of State for Exiting the European Union EU:C:2018:999; [2018] CSIH 62; [2018] CSOH 61; [2018] CSIH 18; [2018] CSOH 8 – CJEU reference from the CSIH on whether the UK’s notification of intention to leave the EU under Article 50 TEU was unilaterally revocable by the UK during the notice period set out in the Treaty. Written and oral submissions on behalf of the Wightman petitioners.
5. Case C-333/14 Scotch Whisky Association and others v. Scottish Ministers EU:C:2015:845 – CJEU reference from the CSIH re compatibility of minimum pricing for alcohol with the principle of the EU free movement of goods/Common Agricultural Policy. Written and oral submissions on behalf of the Scotch Whisky Association petitioners
6. Case C-20/00 Booker Aquaculture (t/a Marine Harvest McConnell) v. Scottish Ministers EU:C:2003:397 – CJEU reference from the CSIH on whether there was an EU law right to compensation in respect of losses arising from public health/disease control measures. Written and oral submissions on behalf of the Booker Aquaculture petitioners.
Education/Career/Memberships
Dec 2023 – Aug 2026 Honorary Professor, University of St Andrews and the School of History’s Institute of Legal and Constitutional Research.
2016-2022 Equality and Human Rights Commission “A” Panel (both Scotland and England & Wales) of senior counsel
2017 Fee paid (part-time) Chair of the First Tier Tribunal for Scotland – Housing and Property Chamber
2015 Fee paid (part-time) Chair of the First Tier Tribunal of the Scottish Tax Tribunal
2009-2013 Chairman of the Edinburgh Centre for Constitutional Law and Honorary Fellow in the School of Law, University of Edinburgh
2008 and 2009 Teaching Fellow in the Law and Public Affairs Program at Princeton University, NJ, USA.
Aidan is the author of a substantial number of academic articles, blog posts and legal practitioner texts including EU law for UK Lawyers (soon to be updated to EU law after Brexit: a guide for the perplexed), and he regularly presents papers at legal conferences and seminars.
Aidan holds the undergraduate degree of LL.B (First Class Hons.) from Edinburgh Law School as well as an LL.M. (First Clas Hons) from the University of Sydney Australia, and an LL.M in International and European law from the European University Institute, Florence. In 2012 he was awarded a doctorate (LL.D.) by the University of Edinburgh on the basis that his publication record was adjudged by an academic panel to have made a substantial and significant contribution to legal scholarship.
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DIRECTORY RECOMMENDATIONS
“Aidan is a brilliant advocate who commands respect in the courtroom.”
He is “a silk who possesses an extraordinary breadth and depth of knowledge.”
Chambers & Partners and Legal 500, 2024
See further:
https://chambers.com/lawyer/aidan-oneill-kc-uk-bar-14:224963
https://www.legal500.com/c/scottish-bar/administrative-and-public-law/silks
https://www.legal500.com/c/scottish-bar/employment/silks
"Aidan is rightly seen as one of the leading silks at the Scottish Bar."
"Aidan O'Neill is one of the very best KCs in terms of commitment and knowledge." "Aidan has a brilliant ability to find a way through even the most complicated legal issues."
"Aidan O'Neill KC is involved in cases of the most profound constitutional significance, appearing before the highest courts in the UK and EU. He specialises in challenges against government policy on public law, human rights or EU law grounds. He is renowned for his willingness to argue difficult cases, predominantly on behalf of petitioners." "Aidan has extraordinarily knowledge of the law which cannot be surpassed by anybody and the ability to find issues in a very creative and thoughtful way. His advocacy is robust and respectful."
"Dual-qualified in Scotland and England, Aidan O'Neill KC possesses experience in important cases on Brexit, employment rights, free movement for EU citizens and the prohibition on trade restrictions between EU member states."
"Aidan O'Neill KC is a walking encyclopedia when it comes to EU law." "Aidan O'Neill KC's knowledge and expertise in Scottish and European law is unparalleled."
"Phenomenal knowledge of all areas with what must be a photographic memory for law, and indeed outside law so that external issues can be brought to bear in legal arguments. A simply extraordinary talent."
"A silk who possesses an extraordinary breadth and depth of knowledge."
"Aidan is a brilliant advocate who commands respect in the courtroom." "Aidan is absolutely the top of his game and the go-to person for a judicial review. His technical knowledge is outstanding and he is also very commercial. He has excellent client care skills too."
"Aidan is a tour de force on his feet. He thinks very quickly and is able to pull together lateral arguments beautifully."
"A huge intellect with a huge capacity for work. If you are looking for counsel who will give it their all, that is Aidan O'Neill KC."
"Aidan is a standout for his human rights work. He has an encyclopedic brain, he is hugely industrious and he is also very user-friendly. His court manner is forceful and robust." "He is a hugely experienced silk. He is very knowledgeable and is really great to work with."
"He is a very tenacious and fearless oral advocate." "He has a phenomenal intellect but is down to earth and easy to work with."
"His forte is in debating the court - he is never satisfied with the final version of an argument and is always looking to improve it."
"Obviously highly regarded, he does a lot of very high-profile cases and is very fiery and passionate."
"Unparalleled knowledge of the area and utter commitment to the piece of work being carried out. The best QC in this field given the breadth and depth of knowledge."
"A very excellent court performer who is good on his feet; he is passionate about the cases he takes on. The fact that he is also qualified in Scotland is a particular bonus for us in that it gives him a good perspective compared to others." "His breadth and depth and knowledge are breathtaking; he surprises me with bits of information all the time."
"Aidan O'Neill QC is demanding and exacting, but what he produces is extraordinary." "He gets a fantastic range of interesting work."
"His breadth and depth is amazing." "He is excellent on his feet, and comes up with very interesting and creative arguments." Chambers & Partners also states that "Aidan is very well known, is excellent on his feet and comes with very interesting and creative arguments." "He is very good on his feet, robust and confident in his position without being bullish."
"His breadth and depth of knowledge both in the law in English law, Scottish law and European law as well as international law is simply mind boggling."
"Extremely user-friendly and supremely swift at getting to the heart of matters." "Experienced and capable of putting together ground-breaking arguments as well as incredibly approachable and helpful." Chambers & Partners also notes that Aidan "has terrific judgement and is very good at reading a court." "The depth and breadth of his legal knowledge is incredible."
"Has phenomenal knowledge of the law."
"His main strength is his ability to consider work or areas of law at short notice and be familiar with them quickly."
"Someone to go to if you have a difficult claimant-side case and want to fight really hard."
"Very helpful and focused. Pays great attention to detail."
"Very knowledgeable and practical in relation to proceedings with a Scottish dimension, and an expert on EU law.” “His written advocacy is excellent. He’s an utterly comprehensive and knowledgeable advocate with virtually unrivalled experience in the higher courts."
"A natural, enthusiastic orator, whose breadth of practice is staggering."
"Knows more about European Law than anyone else and he is incredibly creative with his ideas”. “A heavy hitter, he produces spectacular written notes that show his learning and he is never second bested on them."
"The Supreme Court is his natural forum – he can more than hold his own in that environment and is clearly well-respected there.” “His advocacy skills are tremendous, he is intellectually impressive and he is prepared to take on extremely difficult and notorious work."
"He has an excellent grasp of cutting-edge issues” and “The other side are always extremely intimidated by his knowledge of the law."