Tatiana Siakka is a competition law specialist with wide-ranging experience in both transactional and contentious matters. She is a noted practitioner, with The Legal 500 describing her as an "outstanding competition lawyer" whose "knowledge of the subject is second-to-none". Tatiana advises clients on all aspects of EU and UK competition law and related commercial strategy, and has successfully represented clients before the European and UK courts, as well as before the European Commission and the CMA.

In addition to her transactional practice – routinely handling merger control filings, global FDI screening and clearances under the UK National Security and Investment Act – Tatiana has extensive experience in high stakes competition litigation in the EU and UK courts, including the High Court, the Competition Appeal Tribunal and the Court of Appeal, having acted in seminal and high profile proceedings for both defendants and claimants, including the leading UK authority on unlawful information exchange (Balmoral Tanks v. CMA), as well as two of the largest competition damages claims in the UK – the interchange fees and air cargo litigation – setting a precedent regarding the ability to recover global damages in England.

Tatiana is an appointed member of the Law Society’s EU Committee. She is regularly invited to speak on competition law developments and contributes towards leading competition publications.

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  • Representing a major Polish motorway company in state aid proceedings before the General Court.
  • Advising a member state on its appeal against a General Court judgment concerning state aid proceedings in the healthcare sector.
  • Acting for a performing rights organisation in its complaint to the European Commission for abuse of a dominant position.
  • Acted for Balmoral Tanks Limited as the lead associate in connection with the CMA’s investigation into the supply of galvanised steel tanks for water storage concerning allegations of unlawful information exchange. One of the rare CMA cases comprising both criminal prosecutions and a civil investigation and raising issues of conduct for CMA officials when performing their duties in parallel investigations.
  • Represented Balmoral Tanks Limited in its subsequent appeal against the CMA’s decision before the Competition Appeal Tribunal.
  • Acted for Beckman Coulter and parent company Danaher Corporation as a third-party complainant to the European Commission in relation to the Abbott/Alere merger.
  • Advised the UK’s largest racecourse company in connection with the creation of three joint ventures for the sale of sports media rights.
  • Advised Formula One Management (FOM) on various competition law matters in connection with its pay-TV services.
  • Acted for the parent company of several Italian fashion brands and a professional wrestling media company in connection with the European Commission’s sector inquiry into e-commerce.
  • Advised a US corporation in respect of its claim against a leading kitchenware company for abuse of dominant position through vexatious litigation.
  • Advised on and designed distribution strategies for companies such as Nest Labs, Master&Dynamic, KOSS, GN Netcom, OTB/Diesel and Nutramax, including monitoring and suppressing grey market activity in Europe.
  • Advised several trade associations in the financial, mining and metals sectors, including monitoring and providing advice during meetings, assessing competition law compliance of association activities, publications and communications.
  • Represented a group of more than 500 claimants in their damages claim against British Airways in relation to the worldwide air cargo cartel in the airfreight surcharges. One of the largest competition damages claims, raising novel legal arguments in respect of worldwide damages recovery in England.
  • Represented a group of multinational corporations in their private damages actions arising from unlawful interchange fees against MasterCard and Visa in proceedings before the High Court. A hybrid claim, comprising a follow-on action for intra-EEA interchange fees and standalone claims for domestic fees applicable in 23 jurisdictions.
  • Advised a group of concrete manufacturers in relation to their follow-on claims against cement manufacturing companies. Experience includes strategy planning and coordination of mediation proceedings in a European jurisdiction.


  • BPP Law School, Qualified Lawyer Transfer Scheme, 2014
  • Universiteit Leiden, LL.M., EU and Competition Law, 2012
  • Aristotle University of Thessaloniki, LL.B., 2009
  • Free University of Brussels, Erasmus Scholar, 2007


  • England and Wales, 2015
  • Greece, 2011

Memberships & Affiliations

  • Member of the Law Society’s Competition Law section
  • Member of the Competition Law Association (CLA)


  • English
  • Greek
  • French
  • Recommended in The Legal 500 UK 2023.
  • Recommended in The Legal 500 UK 2022.
  • The Legal 500 UK 2023 interviewees describe Tatiana as “Tatiana Siakka is an outstanding competition lawyer and meticulous in her attention to detail. Her knowledge of the subject is also second to none.”
  • Ranked as a Rising Star in Competition and Antitrust by the Euromoney Expert Guides 2020, 2021 and 2022.

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  • "Labor Collusion Warning Could Signal Enforcement To Come", Law 360 UK, 10 May 2023.
  • “Case C-724/17 Vantaan kaupunki v Skanska Industrial Solutions: Transposition of the Concept of an ‘Undertaking’ into Civil Damages Actions”, Journal of European Competition Law & Practice, 18 November 2019.
  • Redrawing the Market Economy Operator Test: EU State Aid Law Post-Frucona”, European Competition Law Review, August 2018.
  • Hybrid settlements – Cartel facilitation and procedural safeguards in Icap”, Competition Law Insight, 15 March 2018.
  • “EU Commissioner Warns Companies of Potentially Unlawful Use of Pricing Algorithms”, Lexology, 30 March 2017.
  • “European Commission Opens Investigation into Suspected Price Restrictions by Electronic Goods Producers”, Lexology, 7 February 2017.
  • “Football Association Premier League Limited v Luxton [2016] EWCA Civ 1097”, Lexology, 2 December 2016.
  • “Competition and Markets Authority Opens Investigation into Auction Service Providers, Lexology, 28 November 2016.
  • “European Commission’s Preliminary Report in the E-Commerce Sector Inquiry: Highlighting Risk Areas for Suppliers of Branded Goods”, Lexology, 11 October 2016.
  • “ECJ Interprets Rules of Jurisdiction for Cartel Damages Claims”, Legal Media Group’s Expert Guides, 2016.
  • “CJEU Confirms EU Competition Law Does Not Prevent Royalties for Revoked Patent Licences”, Lexology, 14 July 2016.
  • “EU Competition Law Does Not Prevent Royalties for Revoked Patent Licences”, Lexology, May 2016.
  • “‘Eturas’ UAB and Others v. Lietuvos Respublikos konkurencijostaryba”, E-Commerce Law Reports, Vol. 16 Issue 2, April 2016.
  • “CJEU Sends Clear Warning to ‘Cartel Facilitators’”, JD Supra, 29 October 2015.
  • “Keeping up with Competition – Jurisdictional Issues”, Lexis PSL, 14 September 2015.
  • “A summary of recent developments in antitrust damages claims, collective redress and funding in the EU and UK”, Global Competition Litigation Review, 4 July 2013.
  • Contributing author, “Albion v Dër Cymru: Turning the taps on follow-on claims?” Lexis PSL Competition, April 2013.
  • Contributing author, “Consumer opt-outs: a damp squib?”, post on UK Government reforms of private actions in competition law, Kluwer Competition Law Blog, February 2013.
  • “Out of time: the Supreme Court rules on the limitation period for bringing ‘follow on’ damages actions”, Global Competition Litigation Review, 2012.

Speaking Engagements

  • Speaker, “The UK Subsidy Control Act Explained: Interaction With EU Rules”, The Law Society Seminar, 12 July 2022.
  • Speaker, “Overview – Preparing for the Subsidy Control Act 2022: Observations on the UK's forthcoming State Aid regime”, Lexxion, 7 March 2022.
  • Speaker, “State Aid v Subsidy Control Bill – Preparing For Change”, The Law Society Seminar, 21 October 2021.
  • Speaker, “Class Actions – The New Regime”, MBL Seminar, London, 20 June 2016.
  • Speaker, “Package Travel 2.0”, ETOA Conference, London, 18 March 2016.
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