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Mark Sansom

Joint Head – Global Antitrust Litigation Group

Disputes, litigation and arbitration, Global investigations

A very clever lawyer with the ability to unpick the layers

Chambers Leading Individuals 2018

Profile details

About Mark Sansom

Mark is a litigation and antitrust partner in our London office. He leads our London competition litigation team, and jointly leads our global antitrust litigation group and collective and class actions skills group.

Mark advises on both contentious and non-contentious competition matters, with a particular focus on competition/antitrust litigation and investigations.

Mark has a successful track record representing clients in competition investigations by competition authorities in the EU, UK and worldwide, and in 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, including collective proceedings in the CAT. Mark also regularly co-ordinates investigations and litigation arising from the same conduct across multiple jurisdictions.

In addition, Mark acts on market studies and market investigations before the EU and UK competition authorities. He has also 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 influential CAT User Group, which advises the CAT on the development of its Rules and procedures.  He serves as the UK representative on the Advisory Board to the American Bar Association Antitrust Section's Global Private Litigation Committee.  In 2018, Mark was named by Who's Who Legal as one of the global thought leaders in competition litigation.  In 2019, he was voted by peers worldwide as Global Competition Review's Litigator of the Year. 

Recent work

  • Defending Mastercard in the groundbreaking Merricks v Mastercard collective proceedings (class action) before the UK Competition Appeal Tribunal, Court of Appeal and Supreme Court.  The case is reportedly the largest damages claim ever brought in the UK and the Supreme Court's judgment will determine the approach to be applied in all UK antitrust class actions. Read more about the litigation in our case study.
  • 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 sucessfully at trial and prevailed on all points in the October 2019 Court of Appeal judgment. Mark has also acted and is currently acting for ABB in a range of other damages claims relating to the gas insulated switchgear, power transformers and power cables cartels. 
  • Representing London and South Eastern Railway in the Gutmann v LSER proposed 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. 
  • Defending Infineon Technologies in the Vodafone v Infineon & Ors and Gemalto v Infineon & Ors High Court follow-on damages claims arising out of the European Commission's infringement decision in relation to smartcard chips.
  • Acting for SGL Carbon in the Deutsche Bahn and Emerson follow-on cartel damages claims before the Competition Appeal Tribunal.
  • Acting on numerous other competition litigation proceedings, and in investigations, in a range of markets and sectors including automotive, technology, media, financial services, transport and pharma.



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

Professional qualifications

  • English solicitor with higher rights
  • Irish solicitor