Conor is instructed in a wide range of cases concerning competition law, subsidy control and commercial regulation. He has acted for claimants, proposed class representatives, defendants and regulators in matters concerning: cartels; abuse of dominance; the conduct of trade associations; private damages actions; and the enforceability of contractual arrangements in light of competition law requirements and related remedies. He has substantial experience in the fields of jurisdiction, applicable law and the enforcement of foreign judgments. He also has significant knowledge of merger control, having advised, or acted, in a wide range of merger matters: Microsoft / Activision; Sabre / Farelogix; Sky/Fox; Sainsburys / Asda among others.

Conor is frequently instructed to advise, or litigate, on matters of subsidy control (or state aid under the Windsor Framework). He has extensive experience of subsidy control issues arising in a wide range of sectors including energy, environment, telecommunications, research and development, land and property development, public transport, regional development and  public infrastructure projects among others.

He has substantial litigation experience before courts of all levels, including the Supreme Court, Court of Appeal, Competition Appeal Tribunal, all divisions of the High Court as well as the Court of Justice of the EU. He has also been instructed in a number of major arbitrations before the ICC and ICSID.

Conor has been instructed in litigation or advisory work by a wide range of regulators including the CMA, the Financial Conduct Authority, the Payment Systems Regulator, Ofgem, Ofwat, Ofcom and the Trade Remedies Authority. He is often instructed in matters of competition law or commercial regulation raising complex points of public law.

Cases

• ICC Arbitration (confidential): Acting in complex ICC arbitration for major smartphone manufacturer in a FRAND and commercial dispute.
• Flynn and Pfizer v. CMA: counsel to the CMA in lengthy trial of excessive pricing claims in relation to certain pharmaceutical products.
• Microsoft/Activision v CMA: acted for Microsoft in the successful $69bn merger with Activision and the court challenge to the CMA’s initial decision to block the transaction.
• CICCI and CICCII v. Visa and Mastercard: counsel to class representative in proposed collective proceedings against Visa and Mastercard in respect of interchange fees.
• Boots Company plc and Others v Traton SE and Others: Acting for a large group of companies in bringing claims in respect of the trucks cartel in the second wave of trucks proceedings.
• Asda Stores Limited and Others v Bremnes Seashore AS and Others: Acting for Defendant in proceedings brought by UK supermarkets in relation to allegation of a cartel in farmed Atlantic salmon.
• FX Litigation: Counsel for Defendant (RBS) in both collective proceedings and corporate claims in respect of the FX cartel
• Lenzing AG v. Westlake Vinnolit Ltd and others: counsel to Defendants in alleged price fixing cartel.
• Sabre v. Competition and Markets Authority: junior counsel to the CMA in challenge to prohibition decision in merger inquiry.
• Payment Systems Regulator: Advising on a complex cartel investigation.
• Advanz Pharma Corp v. Competition and Markets Authority [2019] EWHC 1605: junior counsel to Advanz in challenge to lawfulness of procedure of CMA’s investigation into abusive pricing in respect of pharmaceuticals.
• Dixons Retail Ltd and ors v. MasterCard Incorporated & ors [2020] EWCA CIV 671 (Court of Appeal): junior counsel for Dixons in complex dispute on limitation as part of the interchange fees litigation.
• Sainsburys v. Competition and Markets Authority: Advising CMA on challenge to CMA’s procedures in Sainsbury’s/ASDA merger.
• 21st Century Fox/Sky – merger inquiry: Advising the Competition and Markets Authority on a wide range of issues concerning the proposed merger between 21st Century Fox and Sky.
• Emerald Supplies Limited v. British Airways and Ors (Air Cargo): Junior Counsel for several hundred corporate claimants in large mutli- jurisdictional damages claim arising from the Air Cargo Cartel.
• Leeds City Council and others v Samsung Electronics Corporation, High Court, Chancery Division: acting for Claimant and advising on various jurisdictional matters in this follow-on damages claim in respect of the operation of the LCD Cartel.
• Hyundai Heavy Industries and ors v. British Airways: Junior Counsel for the Claimants in damages claim based on both EU and foreign law.
• Dixons Retail Limited and another v. MasterCard Incorporated & ors [2015] Comp. A.R. 199: Acting as junior counsel for the Claimant in CAT proceedings, in a claim involving complex issues of private international law jurisdiction and applicable law under both Rome II earlier enactments.
• R (Banks) v Secretary of State for Business, Energy and Industrial Strategy (High Court) (2020): junior counsel for the Secretary of State in a complex state aid challenge concerning the government’s “contracts for difference” scheme to support renewable energy infrastructure in the United Kingdom.
• R (Tempus Energy) v. Secretary of State for Business, Energy and Industrial Strategy (High Court) (2019): junior counsel for the Secretary of State in a state aid judicial review concerning the United Kingdom’s energy capacity market.
• David Haigh v. Gulf Finance House Capital Ltd and ors (High Court, QBD): Instructed by Stephenson Harwood in a complex private international law claim in QBD involving issues of jurisdiction, applicable law and the torts of deceit, conspiracy to injury and unlawful means conspiracy.

Conor has extensive experience of advising businesses and regulators on competition and commercial regulatory issues, including in relation to:

• regulatory investigations by the Trade Remedies Authority in relation to anti-dumping and safeguarding measures.
• regulatory investigations concerning potential breaches of competition law, including by the CMA, PSR and Ofgem.
• the compatibility and validity of contractual terms with competition law and related questions of remedies.
• the legal obligations of companies, and other bodies, who hold a dominant market position.
• complaints to the CMA and European Commission about the conduct of competitors.
• competition and state aid issues arising from new projects or initiatives from central Government and other public bodies.
• competition issues relating to trade organisations and industry bodies.

Ranked as a leading junior in both public law and human rights, Conor has substantial experience in complex civil claims, or judicial review proceedings, involving public authorities.

He is often instructed in heavy commercial regulatory, competition or state aid disputes, by companies, regulators or central government.

He also has significant expertise in matters of data protection and information law (both judicial review and civil claims) as well as in disputes raising questions of international law, including trade law, export control, immunities, human rights, state responsibility, and jurisdictional disputes.

In the field of human rights, Conor has appeared before the European Court of Human Rights on many occasions. He also has considerable experience in the use of international mechanisms including the Optional Protocol to the ICCPR, individual applications in other UN and regional human rights systems as well as in challenges to Interpol Red Notices.

Cases

• Microsoft/Activision v CMA: acted for Microsoft in the successful $69bn merger with Activision and the court challenge to the CMA’s initial decision to block the transaction.
• eBay (UK) Ltd  v. Secretary of State for Business and Trade: counsel to the Secretary of State in relation to eBay’s challenge to a decision by the Office of Product Safety and Standards treating eBay as a distributor for purposes of General Product Safety Regulations 2005 and requiring it to remove products from sale.
• R (Elgizouli) v. Secretary of State for the Home Department (Information Commissioner Intervening) [2020] UKSC 10 (Supreme Court): junior counsel for the Information Commissioner in proceedings concerning information sharing between the United Kingdom and the United States and its compatibility with the Data Protection Act 2018
• Campaign Against Arms Trade v. Secretary of State for Trade [2019] 1 WLR 5765 (Court of Appeal): Junior Counsel for the Claimant in landmark challenge to the legality of continued licensing of arms and military equipment for export to Saudi Arabia on grounds that weapons may be used in serious violations of international humanitarian law.
• Smith v. Talk Talk Telecom Group PLC: Counsel to Claimants in major data protection group action by hundreds of claimants in claims arising from a number of cyber attacks on Talk Talk’s IT systems.
• AK v. Chief Constable of Devon and Cornwall Police (High Court): complex claim against Devon and Cornwall Police for breach of the Data Protection Act 1998, misuse of private information and Article 8, ECHR.
• R (Banks) v Secretary of State for Business, Energy and Industrial Strategy (High Court): junior counsel for the Secretary of State in a complex state aid challenge concerning the government’s “contracts for difference” scheme to support renewable energy infrastructure in the United Kingdom.
• R (Tempus Energy) v. Secretary of State for Business, Energy and Industrial Strategy (High Court): junior counsel for the Secretary of State in a state aid judicial review concerning the United Kingdom’s energy capacity market.
• Western Saharan Campaign UK v. (1) HMRC and (2) Minister for Environment Food and Rural Affairs (High Court) [2016] 1 C.M.L.R. 36 (and C-266/16 R (O.A.O Western Sahara Campaign UK v. Revenue and Customs Commissioners (Grand Chamber) [2018] 3 C.M.L.R. 15: Junior Counsel for Claimant in challenge to legality of the EU-Morocco Association Agreement and the EU Morocco Fisheries Partnership Agreement on grounds of incompatibility with public international law obligations of the EU
• Secretary of State for Work and Pensions v G [2017] EWCA Civ 61 (Court of Appeal): Junior counsel for Claimant in landmark case concerning the interpretation and application of the Vaccine Damage Payment Act 1979.
• R (on the application of T) v Chief Constable of Greater Manchester [2015] A.C. 49 (Supreme Court): Junior counsel for the Equality and Human Rights Commission in the Supreme Court in case concerning disclosure of personal information by police.
• Michael v Chief Constable of South Wales [2015] A.C. 1732 (Supreme Court): Junior Counsel for Welsh Women’s Aid in Supreme Court case concerning scope of protective duty under Article 2, ECHR and also concerning whether the police owe a duty of care in negligence to persons who contact them in an emergency.
• Belhadj v. Security Service [2015] UKIP Trib 13 132-H (IPT): Junior Counsel for the Claimant in a landmark case concerning the interpretation and application of the Regulation of Investigatory Powers Act and the protection under Article 8, ECHR of confidential information, in particular, legally privileged information.
• Chief Constable of South Wales Police v. Daniels and other (Court of Appeal) [2015] EWCA Civ 680, (led by Stephen Cragg KC), landmark judgment of the Court of Appeal on scope of immunity attaching to participants in legal proceedings.
• R (On the application of Catt) v. Association of Chief Police Oicers and Commissioner of Police for the Metropolis [2012] EWHC 1042 (Court of Appeal), junior counsel in intervention on behalf of Liberty in judicial review of decision to retain information on national extremism database in reliance on Article 8, ECHR.
• Girleanu v. Romania, ECtHR, acting alone, represented Guardian News and Media Limited in a third party intervention before the European Court of Human Rights in a case concerning the imposition of sanctions upon a journalist for possession of sensitive information alleged to impinge upon national security.
• Couderc and Hachette Filipacchi v. France, ECtHR (Grand Chamber): acting alone, represented Media Legal Defence Initiative in an intervention before the Grand Chamber of the ECtHR on issues of privacy and free expression.
• David Haigh v. Gulf Finance House Capital Ltd and ors (High Court, QBD): Instructed by Stephenson Harwood in a complex private international law claim in the QBD involving issues of jurisdiction, applicable law and the torts of deceit, conspiracy to injury and unlawful means conspiracy.

Conor is regularly instructed in both private law claims and judicial review challenges in the field of information and data protection law, in cases raising issues concerning the retention, exploitation and disclosure of information. He has particular expertise in issues of confidentiality, including the protection of journalistically privileged material and free expression. He also has substantial experience in complex group claims.

He has been instructed in numerous civil claims raising issues of misuse of personal information, confidentiality and data protection, including claims under the DPA and GDPR.

Cases

• Smith v. Talk Talk Telecom Group PLC: Counsel to Claimants in major data protection group action by hundreds of claimants in claims arising from the extraction of personal data of a large number of customers in a number of cyber-attacks which exploited vulnerabilities in Talk Talk’s IT systems.
• R (Elgizouli) v. Secretary of State for the Home Department (Information Commissioner Intervening) [2020] UKSC 10 (Supreme Court): junior counsel for the Information Commissioner in proceedings concerning information sharing between the United Kingdom and the United States and its compatibility with the Data Protection Act 2018
• Big Brother Watch and others v. the United Kingdom, ECtHR Grand Chamber (2020): counsel for Bureau of Investigative Journalism in challenge to legality of regime in Regulation of Investigatory Powers Act 2000 for interception, storage, dissemination and destruction of journalistically privileged information.
• R. (on the application of T) v Chief Constable of Greater Manchester [2015] A.C. 49 (Supreme Court): Junior counsel for the Equality and Human Rights Commission in the Supreme Court in case concerning disclosure of personal information by police.
• AK v. Chief Constable of Devon and Cornwall Police (High Court): counsel in complex claim against Devon and Cornwall Police for breach of the Data Protection Act 1998, misuse of private information and Article 8, ECHR.
• R (On the application of Catt) v. Association of Chief Police Officers and Commissioner of Police for the Metropolis (Court of Appeal): intervention on behalf of Liberty in judicial review of decision to retain information on national extremism database, in reliance on Article 8, ECHR.
• Kupiec v. National Crime Agency and Chief Constable of West Mercia Police: Complex claim arising from the detention and imprisonment of a foreign national wrongly identified as wanted for extradition in a murder case.
• Sheriff v. HMCTS and Chief Constable of Derbyshire: successful claim against both Defendants in a complex damages action for breach of the DPA, Article 8, ECHR and Article 5, ECHR.
• Girleanu v. Romania, ECtHR, acting alone, represented Guardian News and Media Limited in a third party intervention before the European Court of Human Rights in a case concerning the imposition of sanctions upon a journalist for possession of sensitive information alleged to impinge upon national security.
• Couderc and Hachette Filipacchi v. France, ECtHR (Grand Chamber): acting alone, represented Media Legal Defence Initiative in an intervention before the Grand Chamber of the ECtHR on issues of privacy and free expression.
• Belhadj v. Security Service [2015] UKIP Trib 13 132-H (IPT): Junior Counsel for the Claimant in a landmark case concerning the interpretation and application of the Regulation of Investigatory Powers Act and the protection under Article 8, ECHR of confidential information, in particular, legally privileged information.

Conor has considerable experience of issues of general international law. He has been instructed in a range of international courts, tribunals, including the International Court of Justice, as well as in arbitral proceedings.

In the field of human rights, he has considerable experience in cases utilising international mechanisms, including applications to the Human Rights Committee under the Optional Protocol to the ICCPR, as well as other UN and regional human rights treaties, including the ECHR where he has appeared on numerous occasions. He has also been instructed in applications for the deletion and removal of Interpol Red Notices.

As regards international trade law in particular, Conor has experience advising on a range of areas including market access, MFN and national treatment issues, issues of treaty interpretation in the trade context (as well as in the context of a range of other international law disputes). Recent advisory work in the field of trade includes significant advisory work for the Westminster and Welsh Governments on a issues regarding WTO agreements. He is instructed by trade associations as well as companies to advise on issues of trade and export control as well as supply chain obligations and due diligence.

Prior to coming to the Bar Conor completed a PhD in international law at Cambridge University, where he also taught international law.

Cases

• Advising UK’s trade remedies authority in relation to a number of safeguards and anti-dumping investigations.
• Costa Rica v. Nicaragua (Certain Activities Carried Out By Nicaragua in the Border Area) (Reparation Phase): instructed as junior counsel to Costa Rica in claim for reparation before International Court of Justice arising from, inter alia, environmental harm caused by breach of international obligations by Nicaragua
• Campaign Against Arms Trade v. Secretary of State for Trade [2019] 1 WLR 5765 (Court of Appeal): Junior Counsel for the Claimant in landmark challenge to the legality of continued licensing of arms and military equipment for export to Saudi Arabia on grounds that weapons may be used in serious violations of international humanitarian law.
• Western Saharan Campaign UK v. (1) HMRC and (2) Minister for Environment Food and Rural Affairs (High Court) [2016] 1 C.M.L.R. 36 (and C-266/16 R (O.A.O Western Sahara Campaign UK v. Revenue and Customs Commissioners (Grand Chamber) [2018] 3 C.M.L.R. 15: Junior Counsel for Claimant in challenge to legality of the EU-Morocco Association Agreement and the EU Morocco Fisheries Partnership Agreement on grounds of incompatibility with public international law obligations of the EU
• David Haigh v. Gulf Finance House Capital Ltd and ors (High Court, QBD): Instructed by Stephenson Harwood in a complex private international law claim in the QBD involving issues of jurisdiction, applicable law and the torts of deceit, conspiracy to injury and unlawful means conspiracy.
• UK National v. State Official from Middle Eastern State (confidential): Advised the claimant on state immunity in respect of a potential private international law civil claim.
• Jones v. the United Kingdom, ECtHR: Landmark case before the European Court of Human Rights (Grand Chamber) concerning State immunity and Article 6, ECHR.
• Zubaydah v. Lithuania, ECtHR: work for Interights in case concerning extraordinary rendition, extraterritorial jurisdiction and torture.
• Garzon v. Spain, ECtHR: Produced an expert opinion with James Crawford SC on permissibility under international law of application of limitation periods in respect of grave violations of international human rights law.
• Matua & Others v Foreign and Commonwealth Office: the ‘Mau Mau’ litigation, relating to claims for colonial-era ill-treatment in Kenya.
• Haquim v. Secretary of State for Defence (High Court, Administrative Division): led by Martin Westgate KC, claim relating to the transfer of Afghan detainees from UK custody to Afghan detention.

Recent advisory work includes:

• Advice for a trade association in respect of certain public international law trade issues arising from Brexit.
• Advising a governmental body on certain international law issues in connection with Brexit.
• Advising a Caribbean State in connection with potential international litigation

Conor has considerable expertise of issues of private international law. He regularly advises on private international law claims, particularly in connection with tortious liability, including applicable law, the application of foreign law, jurisdiction, procedural issues arising in such litigation as well as issues arising under Rome II Regulation (EC) No 864/2007. He has advised in relation to such proceedings both inside and outside the EU, including a variety of States in the Middle East.

Administrative and Public Law: “Conor is a fierce intellect. He has an amazing ability to construct arguments and to play through how arguments might develop.” “Conor is intellectually outstanding.” “Conor McCarthy is good with international law elements.” – Chambers UK, 2025

Civil Liberties and Human Rights: “Conor is really dedicated. He get stuck in and does the work.” – Chambers UK, 2025

Competition: “Conor McCarthy has a level of expertise that far outstretches his year of call.” “Conor McCarthy is very smart and very hard-working.” – Chambers UK and Chambers Global, 2025

Data Protection: “Conor is highly knowledgeable. He is quick to grasp complex legal and factual issues and is always on top of the documents. He is a pleasure to work with.” “Conor has a genuinely creative flare. He looks substantially at proper solutions to a case.” “Conor is unbelievably clever. He has first-rate market knowledge. He is very good in writing and is good with clients.” – Chambers UK, 2025

Leading Junior in Administrative Law and Human Rights: “Clever, even in an area with lots of clever barristers.” – Legal 500, 2025

Leading Junior in Competition: “Conor is forensic, extremely intelligent and very well read. His analyzation skills are exemplary and his overall knowledge of competition law and public law make for an excellent combination when it comes to producing legal advice.” – Legal 500, 2025

Administrative and Public Law: “Conor is very hard-working and insightful, and he knows all the latest developments.” “He is an exceptionally bright individual.” – Chambers UK, 2024

Civil Liberties and Human Rights: “He is extraordinarily bright; he starts off with an academic overview of the case and proceeds to the practical. He is able to talk through what the changes are and their practical consequences. His work product is comprehensive.” – Chambers UK, 2024

Competition: “He has a very clear mind and is an excellent draughtsperson. It’s been a pleasure to work with him. Having him has been a massive addition to the skillset of the team and he’s been incredibly supportive.” – Chambers UK, 2024

Data Protection: “He is a clever man and his work product is absolutely comprehensive.” – Chambers UK, 2024

Leading Junior in Competition: “Conor is forensic, highly knowledgeable and always helpful and approachable. He is the go-to senior junior for competition law.” – Legal 500, 2024

Leading Junior in Administrative Law and Human Rights: “A diligent junior with good judgement.” – Legal 500, 2024

Administrative and Public Law: “Phenomenally clever. He is really enthusiastic, hard-working and utterly reliable.” – Chambers UK, 2023

Civil Liberties and Human Rights: “He is incredibly academic. He works very hard and is utterly reliable.” “Conor is really strategic, and knows how to run and structure complex judicial review claims.” – Chambers UK, 2023

Data Protection: “He has wise and strategic insight and is a very good tactical litigator, so he knows when or when not to run a point.” “Conor McCarthy is very knowledgeable in the area and is flexible.” – Chambers UK, 2023

Leading Junior in Competition: “Conor is an outstanding barrister who possesses an incisive mind and great courage in his convictions. He develops his views and advice carefully and rigorously and is more than able to defend it robustly, even in difficult contexts. His written advocacy is similarly exceptional and he has the ability to produce clear and compelling drafting within short time constraints.” – Legal 500, 2023

Leading Junior in Administrative Law and Human Rights: “Conor is excellent with matters of general public law and always willing to think outside the box, often coming up with creative solutions.” – Legal 500, 2023

Administrative and Public Law: “He has very sharp instincts and judgement and identifies salient legal points.” “An incredibly approachable barrister and really nice to work with for all members of a team.” – Chambers UK, 2022

Civil Liberties and Human Rights: “He knows exactly where he can make arguments stick.” – Chambers UK, 2022

Leading Junior in Competition: “Highly responsive and a pragmatic problem solver.” – Legal 500, 2022

Leading Junior in Administrative and Public Law: “He has complete attention to detail, and seems to find time to draft or advise even at short notice in urgent matters. His focus is always on the best result for the client.” – Legal 500, 2022

Administrative and Public Law: “He’s got an incredible intellectual mind and is probably one of the most thorough juniors I have come across. He’s also started to work on some pretty important cases.” “If we have another judicial review I would have zero hesitation in calling him again – he clearly knows the subject and I have been very impressed with his work.” – Chambers UK, 2021

Civil Liberties and Human Rights: “He really understands the area well.” – Chambers UK, 2021

Leading Junior in Competition: “He is enthusiastic and inventive. Easy to work with.” – Legal 500, 2021

Leading Junior in Administrative and Public Law: “He is intelligent, knowledgeable and inventive.” – Legal 500, 2021

Administrative and Public Law: “I’d highly recommend him for any judicial review with international elements. He’s one of the few people who really understands this niche area well.” “He provides very thorough, detailed and comprehensive advice.” – Chambers UK, 2020

Civil Liberties and Human Rights: “A good junior and pleasant to work with.” – Chambers UK, 2020

Administrative and Public Law: “An excellent drafter and an excellent advocate.” “Has a very impressive background as an academic and is a very good lawyer with substantive knowledge.” – Chambers UK, 2019

Civil Liberties and Human Rights: “An effective human rights lawyer.” – Chambers UK, 2019

Administrative and Public Law: “He is very thorough and compelling.” – Chambers UK, 2018

Civil Liberties and Human Rights: “Very quick, efficient and helpful.” “He is a very impressive international human rights specialist.” – Chambers UK, 2018