"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."