Catherine Arnold

Contact Catherine: CatherineArnold@matrixlaw.co.uk | +44 (0)20 7404 3447

Contact Catherine's Practice Team (Team X): TeamX@matrixlaw.co.uk

Catherine accepts instructions in all of Matrix’s practice areas, with an emphasis on group litigation and private international law, public law and human rights, actions against the police and prison authorities, media law, and education law.

Group Litigation / Private International Law

Catherine is developing expertise in private international law claims and domestic group litigation:

• NOx Emissions Group Litigation – Acting for the claimants in the high-profile NOx Emissions Group Litigation arising out of 16 major car manufacturers’ alleged use of in-car ‘defeat devices’ (as a member of the claimants’ Counsel team led by Tom de la Mare KC, Oliver Campbell KC, Ben Jaffey KC, and Adam Kramer KC). Instructed in a 10-week trial in the litigation starting in October 2025.
• Various Claimants v Shell plc & Renaissance Africa Energy Company Ltd – Acting for two Nigerian communities in litigation against Shell’s UK-based parent company and its Nigerian subsidiary in respect of alleged systemic and ongoing environmental pollution from Shell’s operations (as a member of the claimants’ Counsel team led by Phillippa Kaufman KC and Anneliese Day KC). Instructed in a preliminary issue trial of Nigerian law issues in February 2025 (Alame and ors v Shell plc and Renaissance Africa Energy Company Ltd [2025] EWHC 1539 (KB)); and in CMCs in the litigation (including Alame v Shell plc [2026] EWHC 2332 (KB)).
• Group Litigation against Grindr – Acted for the claimants in group litigation against Grindr alleging that the company shared UK users’ sensitive personal information, including in some cases their HIV status, with third parties for commercial purposes. Grindr agreed to pay £26 million to settle the litigation. The settlement included no findings or admissions of liability (led by Catrin Evans KC, with Ian Helme).

Public Law and Human Rights

Catherine has experience in a range of public and administrative law matters at all stages of proceedings, including pre-action advice, interim relief, and appeal. Her recent work has been in the areas of: (i) national security; (ii) immigration; (iii) prisons; and (iv) community care (acting in proceedings before the Court of Protection). Notable cases include:

• R (Sahayb Abu) v Secretary of State for Justice [2025] EWHC 3026 (Admin). Acted for the claimant in a judicial review claim of the Secretary of State’s repeated decisions to segregate him following an attack on prison officers by another prisoner on 12 April 2025. The decision was held to violate Articles 3 and 8 ECHR and to be unlawful on a number of public law grounds (led by Tim Owen KC, with Tim James-Matthews and Zoe Brereton).
• Yang Tengbo (formerly H6) v Secretary of State for the Home Department (SC/205/2023). Acted for the applicant in a Special Immigration Appeals Commission (“SIAC”) review raising complex issues of procedural fairness (led by Hugh Southey KC).
• H6 v Special Immigration Appeals Commission. Acted for the claimant in a judicial review claim concerning open justice in the SIAC context (led by Hugh Southey KC and Guy Vassall-Adams KC).

Prison Law / Police Law / Inquests

Prison law

Catherine regularly acts for prisoners, including national security prisoners, in public law and private law claims against prison authorities. Her experience includes acting in judicial reviews of security risk categorisation decisions and of Rule 45 segregation decisions in the Separation Centre context; in civil claims against prison authorities including under the Human Rights Act 1998; and in proceedings before the Parole Board.

Notable cases include:

• R (Abu) v Secretary of State for Justice [2025] EWHC 3026 (Admin). Acted for the claimant in a judicial review claim of the Secretary of State’s repeated decisions to segregate him following an attack on prison officers by another prisoner on 12 April 2025. The decision was found to violate Articles 3 and 8 ECHR and to be unlawful on a number of public law grounds (led by Tim Owen KC, with Tim James-Matthews and Zoe Brereton).
• Acted for the claimant in a judicial review claim of the Secretary of State for Justice’s refusal to downgrade him from Category A. Shortly before the hearing of the claim, the Secretary of State accepted that when undertaking a Category A security risk categorisation review, he is under a duty to attempt to resolve disputed factual allegations which are material to the decision (i.e., those that go to the issue of risk). This is an important extension of the principles in R (De Silva) v Secretary of State for Justice [2025] EWHC 128 (Admin) and R (Pearce) v Parole Board [2023] AC 807 (SC) (led by Jesse Nicholls, with Roz Comyn).

Actions against the police

Catherine also accepts instructions in actions against the police. Her work includes:

• Fourness v BTP and Met Police – successfully resisted the Second Defendant’s application for strike out and/or summary judgment of the claimant’s claims for malicious prosecution and misfeasance in public office.
• MNZ v Essex Police – successful application for early specific disclosure arising out of claims under Article 3 ECHR for errors in police investigation relating to serious racially aggravated assault on teenage boy.

Catherine has experience in inquests and related public law matters. Her work includes acting for the claimant in a judicial review of an inquest raising novel points of law in respect of a coroner’s power to hold an inquest in writing under s.9C of the Coroners and Justice Act 2009, which was granted permission by the Administrative Court (led by James Robottom). During traineeship, she assisted with a PIRH in an Article 2 inquest.

Media Law

Catherine accepts instructions in all aspects of media law. Notable cases include:

• Group Litigation against Grindr – Acted for the claimants in group litigation against Grindr alleging that the company shared UK users’ sensitive personal information, including in some cases their HIV status, with third parties for commercial purposes Grindr agreed to pay £26 million to settle the litigation. The settlement included no findings or admissions of liability (led by Catrin Evans KC, with Ian Helme).
• Yang Tengbo (formerly H6) v Secretary of State for the Home Department (SC/205/2023). Acted for the applicant in proceedings arising out of the media’s request for access to court documents in a SIAC review (led by Guy Vassall-Adams KC).
• H6 v Special Immigration Appeals Commission. Acted for the claimant in a judicial review claim concerning open justice in the SIAC context (led by Hugh Southey KC and Guy Vassall-Adams KC).

Catherine also has experience in pre-publication work and has completed a placement with the in-house legal team at The Times and The Sunday Times. She has written for INFORRM and the Entertainment Law Review.

Education Law

Catherine accepts instructions in all aspects of education law. Her experience includes advising a higher education provider on responding to a regulatory decision (led by Nick Armstrong KC) and acting in proceedings before the SEND Tribunal.

Background and Education

Prior to joining Matrix, Catherine completed her Ph.D., with Distinction, in History at Yale University and was Assistant Professor of History at the University of Memphis in Tennessee. Her research and teaching focused on the history of international human rights and humanitarian intervention. Her first book, Affairs of Humanity: The Religious Origins of Humanitarian Diplomacy in Britain and Europe, 1690-1748, was published by Yale University Press in November 2025.

Qualifications and Awards: 

• B.A., Italian Studies, Wellesley College (2010) – First Class (ranked in top 2% of year group); awarded Departmental Honours for senior thesis.
• Ph.D., History, Yale University (2017) – Distinction (won the Hans Gatzke Prize for Outstanding Dissertation in European History).
• Graduate Diploma in Law, City, University of London (2022) – Distinction (awarded City, University of London’s top merit scholarship; Gray’s Inn Enoch Dumbutshena GDL Scholarship).
• Bar Vocational Studies Course, City, University of London (2023) – Distinction (awarded Gray’s Inn Prince of Wales Scholarship; City Law School Scholarship for Academic Excellence).

Catherine speaks an advanced level of French and Italian.

Professional Memberships

• Lawyers Who Care (mentor)
• Young Legal Aid Lawyers
• Young Public Lawyers Group
• Constitutional and Administrative Law Bar Association

Testimonials

Catherine’s abilities far, far exceed her call; she became an indispensable member of the legal team on a case of importance, complexity and public profile. Her drafting and analytical skills, and ability to perform under pressure, have been impressive and greatly appreciated by the client and instructing solicitors. Adam Glass, Lewis Silkin

Catherine was part of the team a complex foreign law trial which concerned the horizonal application of constitutional rights to corporations in environmental claims.  She worked incredibly hard and assisted with reviewing all the expert reports and with the drafting of superb opening and closing submissions.  She is a pleasure to work with and has a bright future at the Bar. Daniel Leader, Leigh Day

Catherine did a fantastic job of identifying and explaining key issues and concepts from very large volumes of complex material. She is highly intelligent and has excellent analytical and drafting skills. She is also very hard-working, reliable and a pleasure to work with. Matthew Renshaw, Leigh Day

Catherine is committed to protecting and respecting your privacy. In order to provide legal services to her clients, including advice and representation services, Catherine needs to collect and hold personal data. This includes her client’s personal data and the personal data of others who feature in the matter upon which she is instructed. To read Catherine’s privacy notice in full, please see here