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Mark Sansom

London and Dublin Managing Partner

Antitrust and competition | Commercial litigation | Investigations | Mass claims |

Mark is the best competition litigator in the business

Client, Chambers UK 2024

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About Mark Sansom

Mark is a litigation and antitrust partner in our London office. He is the Managing Partner of the Freshfields London and Dublin offices.

Mark practises fully alongside his role as Freshfields' London Managing Partner.  He advises on both contentious and non-contentious competition matters, with a particular focus on competition/antitrust litigation and investigations.

Mark has unsurpassed experience defending clients from damages actions before the UK courts and Competition Appeal Tribunal (CAT). He has acted on many of the leading UK competition damages cases, and has particular experience in collective proceedings in the CAT, acting on the defence side of the defining matters. Mark also regularly co-ordinates investigations and litigation arising from the same conduct across multiple jurisdictions, including on a pan-European or global basis.

In addition, Mark acts on competition/antitrust investigations in the UK, EU and beyond, and on market studies and market investigations before the EU and UK competition authorities. He has advised on arbitrations involving competition law issues (under ICC and UNCITRAL rules) and has appeared as an advocate before arbitral tribunals.

Mark is a member of the CAT User Group, which advises the CAT on the development of its Rules and procedures.  He has previously held roles on the ABA's Antitrust Global Private Enforcement Committee. 

He is a top-ranked practitioner in all the leading directories and named in Chambers as a Global Elite Thought Leader in both the Competition and Firm Management fields.  In 2019, he was voted by peers worldwide as Global Competition Review's Litigator of the Year.  He was featured in The Lawyer's 'Hot 100' list of leading lawyers for 2024. 

Recent work

  • Defending Mastercard in the leading Merricks v Mastercard collective proceedings (class action) before the UK Competition Appeal Tribunal, UK Court of Appeal and UK Supreme Court.  The case is reportedly the largest damages claim ever brought in the UK and is continuing to shape the approach to all UK antitrust class actions. Read more about the litigation in our case study.
  • Mark is also defending Mastercard in the separate Commercial Cards collective proceedings in the CAT and in the Merchant Umbrella Proceedings.  
  • Representing London and South Eastern Railway in the Gutmann v LSER collective proceedings concerning rail tickets, the first standalone and first alleged abuse of dominance related collective proceedings brought in the Competition Appeal Tribunal under the UK's competition class action regime.
  • Acting for Govia Thameslink Railway in the Gutmann v GTR and Boyle v GTR opt-out collective proceedings, also standalone abuse claims concerning rail tickets. 
  • Acting for ABB in the leading BritNed v ABB High Court action and in the Court of Appeal. The case was the first cartel damages follow-on claim to go to final judgment at first instance, and on appeal, in the UK.  ABB defended the claim successfully at trial and prevailed on all points in the October 2019 Court of Appeal judgment. Mark has also represented ABB in a range of other damages claims relating to the gas insulated switchgear, power transformers and power cables cartels. 
  • Successfully defending Infineon Technologies in the UK High Court and Court of Appeal in the Gemalto v Infineon & Ors High Court follow-on damages claim arising out of the European Commission's infringement decision in relation to smartcard chips.  The case is now a leading authority on limitation.  
  • Acting on numerous other competition litigation proceedings, and in investigations, in a range of markets and sectors including water, automotive, technology, media, financial services, sport, transport and pharma.



  • LLB English Law and French Law
  • Postgraduate Diploma in EC Competition Law

Professional qualifications

  • English solicitor with higher rights
  • Irish solicitor