Diarmuid Ryan is a partner and global chair of our Competition – Antitrust Practice based in our London and Brussels offices. Diarmuid specialises in all aspects of EU and UK competition and state aid law.

His expertise includes:

  • Advising on global competition authority investigations into cartels, collusion and abuse of dominance, including, in particular, investigations by the UK competition authorities and the European Commission.
  • Advising on global competition issues arising in relation to mergers, joint ventures and strategic alliances.
  • Advising on the competition aspects of various types of commercial agreement such as distribution agreements, technology transfer agreements, joint production, outsourcing, research and development and specialisation agreements.
  • Advising on the compatibility of various forms of central/regional/local government assistance/support with the EU/UK state aid/subsidy rules.
  • Advising on competition-based disputes and litigation, including judicial review of regulatory decisions.

Diarmuid specialises in competition compliance advice, including advising on compliance programs and dawn raid programs, devising and undertaking competition compliance audits, and devising and undertaking mock dawn raids. He also serves as a member of the firm’s Advancing Women Task Force.

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  • Advising Tereos SCA on the CMA’s ongoing review of the sale of its UK B2C business to Tate & Lyle.
  • Advising Pharmacy2U on the CMA’s ongoing review of its acquisition of Lloyds Direct.
  • Advising Pets at Home Group Plc on the CMA’s ongoing sector review of the veterinary market for pets launched in September 2023.
  • Advising Blackhall Facilities Management on the Irish CCPC’s merger control review of its acquisition by Inflexion, which was cleared unconditionally on 21 December 2023.
  • Defending one of the parties under investigation in the CMA’s ongoing end-of-life vehicles cartel investigation launched in March 2022.
  • Advising Blackhall Facilities on the Irish Competition and Consumer Protection Commission’s 2022 investigation of the proposed sale of its Village Vets veterinary clinics business to Linnaeus Veterinary Limited, Ireland.
  • Advising Kongsberg Automotive Group in securing unconditional Phase 1 clearance from the European Commission in February 2022 for the sale of its interior comfort systems business to Lear Corporation.
  • Advising Grafton Group plc on the CMA’s review of the £520 million sale of its traditional merchandising business in Great Britain to Huws Gray, which was cleared in January 2022 subject to Phase 1 undertakings.
  • Advising Studio Retail Group plc on the CMA’s Phase 1 and Phase 2 reviews of the sale of its Findel Education business to YPO.
  • Advising a global provider of market research/media analysis on the CMA’s market study into outline platforms and digital advertising.
  • Advising Funeral Partners on the CMA’s market investigation into the supply of funeral directors services and crematoria services.
  • Advising Vp plc in the CMA’s antitrust probe in the construction equipment sector (groundworks).
  • Advising Send For Help Limited on the CMA’s review of its proposed acquisition of Solo Protect in March-May 2019.
  • Advising a global supplier of branded FMCG products on the CMA’s Phase 2 merger control review of the proposed Sainsbury’s/Asda merger, which was prohibited on 25 April 2019.
  • Advising Lane Clark and Peacock LLP on the CMA’s market investigation into investment consultancy services and fiduciary management services. The CMA adopted its final report on 12 December 2018.
  • Advising A.C Nielsen on the CMA’s Phase 1 and Phase 2 merger control review of its proposed acquisition of Ebiquity Plc’s AdIntel business. The CMA unconditionally cleared this transaction on 22 November 2018.
  • Advising Auction Technology Group on the CMA’s merger control review of its completed acquisition of lot-tissimo. The CMA unconditionally cleared this on 12 July 2018.
  • Advising GET ME IN! and Seatwave on the CMA’s secondary ticketing investigation. On 25 April 2018, the CMA announced it had accepted undertakings from GET ME IN! and Seatwave (and from StubHub).
  • Advising Vp Plc on the CMA’s merger control review of its completed acquisition of Brandon Hire, which was cleared unconditionally on 7 March 2018.
  • Advising Cott Beverages on the CMA’s merger control review of the anticipated acquisition by Refresco of Cott’s traditional beverages business. On the 29 March 2018, the CMA decided to accept a Phase 1 divestiture remedy regarding the parties’ overlapping A-PET juice drinks business, thereby avoiding a Phase 2 review.
  • Advising ATG Media in successfully defending itself against a CMA Article 101/102 probe in the auction house service sector, launched in November 2016. On 29 June 2017, the CMA accepted commitments from ATG Media, with no finding of infringement.
  • Advising Yorkshire Provender Ltd on the CMA’s merger control review of its acquisition by Hain Frozen Foods. The CMA unconditionally cleared this transaction on 20 April 2017.
  • Advising Ashtead Group plc on the CMA’s merger control review of its acquisition of Lion Trackhire Limited, which was unconditionally cleared on 25 August 2016.
  • Successfully advising Peninsula Business Services on the CMA’s merger control review of its completed acquisition of Croner Group. This was cleared unconditionally on 9 May 2016.
  • Successfully defending a branded bathroom fittings company on the CMA’s probe into suspected anticompetitive practices in the bathroom fittings sector, which was launched on 28 August 2014 and closed (as regards our client) in May 2016.
  • Advising Poundworld in relation to the CMA’s Phase I and Phase II review of the Poundland/99p Stores merger in 2015 (February-October).
  • Advising a pan-European manufacturing business in designing and implementing a comprehensive corporate compliance policy as regards all material regulatory risk facing the business.
  • Advising Marston Holdings on the CMA’s review of its completed acquisition of the Collectica debt management business, which was unconditionally cleared on 26 November 2014.
  • Advising a third-party complainant in successfully challenging before the Competition Appeal Tribunal (CAT), the UK Office of Fair Trading’s (OFT) late-2013 merger control clearance of the completed IRi/Aztec merger in the retail data sector. This was the first successful judicial review challenge to a UK Phase I merger clearance decision in more than a decade. Also advised this client during the CMA’s reconsideration of the merger, on remittal from the CAT.
  • Advising Ashland Inc. on the non-US merger control aspects of the sale of its Water Technologies business to Clayton, Dubilier & Rice, announced on 18 February 2014. Unconditional merger control clearances were secured from the European Commission and from the merger control authorities in China, Taiwan, South Korea, Russia and Canada.
  • Advising Cott Developments Ltd. on the merger control aspects of its acquisition of the Calypso and Mr Freeze soft drinks brands, including obtaining unconditional OFT clearance on 25 June 2013.
  • Conducting a general antitrust audit for one of Europe’s largest mobile telecoms networks.
  • Advising a third-party complainant in respect of the DS Smith/SCA Packaging merger, which on 5 July 2012 the European Commission subjected to a detailed remedies package as a condition of clearance.
  • Advising Cytec Industries Inc. on the merger control aspects of its public bid for Umeco plc, which was unconditionally cleared by the European Commission on 11 June 2012.
  • Advising The Book Depository on the global merger control aspects of its November 2011 acquisition by Amazon.com. This involved obtaining merger control approvals in Australia, Austria, Cyprus, Ireland, Malta and the UK.
  • Advising SSP Limited on the OFT's Motor insurers data exchange investigation. On 2 December 2011 the OFT formally accepted commitments offered by SSP and the other firms under investigation and its investigation without any finding of infringement.
  • Advising Atlas Copco Limited in obtaining unconditional clearance from the OFT on 7 July 2011 in respect of its acquisition of the medical gas division of Penlon Limited, which involved the first use by the OFT of certain aspects of its new guidance on exceptions to the duty to refer.
  • Advising Chelsea FC in defending against Adrian Mutu’s complaint to the European Commission that the award against him and in favour of the club of €17 million in compensation for breach of contract, infringed Articles 45, 101 and 102 TFEU. The European Commission closed its file in April 2011 following the withdrawal of the complaint.
  • Advising BSS Group, a major plumbing and heating company, on the competition law and merger control aspects of its proposed £557.6 million takeover by Travis Perkins, one of the UK’s largest builders’ merchants. The transaction was notified to the OFT on 16 July 2010 and on 26 October 2010 the OFT announced its decision not to refer the transaction to the Competition Commission subject to the sale of branches in 20 local areas.
  • Advising Aldi Stores Limited on the Competition Commission's Groceries Market investigation (2006-2010) and subsequent implementation of remedies imposed and monitored by the OFT.
  • Advising Lucite International on the merger control aspects of its US$1.6 billion acquisition by Mitsubishi Rayon Co. Ltd., involving filing in Spain, Portugal, Turkey, Germany, South Korea and Taiwan, as well as a Phase II merger review in China. This transaction completed on 28 May 2009 following acceptance by MOFCOM (Chinese regulator) of an innovative remedies package.
  • Advising on the Phase I (OFT) and Phase II (UK Competition Commission) merger control review of INEOS Chlor Limited’s proposed sale of its packaged chlorine business and assets to BOC Limited.
  • Advising INEOS Chlor on its successful defence of an investigation by the European Commission during 2007-2008 into alleged gun-jumping, including representing INEOS onsite during the course of a Commission dawn raid.
  • Advising Live Nation Inc. and Gaiety Investments on the UK Competition Commission’s Phase II merger control review of their joint acquisition of the Academy Music Group (Competition Commission clearance decision dated January 2007 and final undertakings accepted in February 2007).


  • College of Law, York, L.P.C., 1996
  • College of Europe, Bruges, LL.M., 1995
  • University of Cambridge, Emmanuel College, B.A. in Law, 1994


  • Brussels Bar (A List), 2023
  • Brussels Bar (EU List), 2019
  • Ireland (Certificate of Attestation), 2017
  • England and Wales, 1998


  • English
  • Recommended as a Leading Individual and Hall of Fame member for EU and Competition (London), Diarmuid is described as “providing highly practical and commercial advice delivered straight” and as enjoying “a stellar reputation on account of his far-reaching EU and UK competition expertise” The Legal 500 UK 2023
  • Recommended for Competition Law, London, Chambers UK 2023
  • Recommended in Who’s Who Legal: Competition 2022 (England)

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  • Co-author, “Pharma Sector: Long a Target for Antitrust Enforcers,” European Pharmaceutical Review, Vol. 3, 2016.
  • Author, “Why UK Backed Off From Loyalty Rebate Abuse Probe,” Law360, 29 July 2015.
  • Author, “Platform Price Parity Clauses: Various UK-led investigations,” E-Commerce Law & Policy, November 2013.
  • Co-author, “The World Has Changed: Global Cartel Enforcement Brings New Risks,” Antitrust & Trade Regulation Report, Bloomberg BNA, Vol.105, No.2618, 11 October 2013. Awarded the prestigious Burton Award for distinguished legal writing.
  • Co-author, “Market Data Supply Agreements,” The European Antitrust Review 2012 (Global Competition Review special report).
  • Co-author, “Assessing Information Exchanged Between Competitors in Light of the New Horizontal Guidelines,” Euromoney Yearbook, Competition & Antitrust Review 2011.
  • Co-author, “The Judicial Application of European Competition Law,” XXIV FIDE Congress Topic 2 Report, November 2010.
  • Co-author, “Abuse of Dominance – When Is an “Excessive’ Price ‘unfair”? Recent Developments at EU and Member State Level,” Euromoney Yearbook, Competition & Antitrust Review 2009.
  • Author, “Weighing Up the Competition,” Legal Week, 13 December 2007.
  • Author, “How National Agencies Approach Defence Mergers,” Global Competition Review 2003.
  • Author, “Abuse of a Dominant Position in EC Competition Law: Recent Developments,” The European Antitrust Review 1999 (Global Competition Review special report).

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