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Marie Demetriou KC

Marie Demetriou KC

YEAR OF CALL: 1995    YEAR OF SILK: 2012

“Marie is an amazing advocate: succinct, precise, and judges are very receptive to her… She wins so often.”
Chambers and Partners 2021
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Marie Demetriou KC is widely recognised as a leading advocate in the fields of competition law, EU law, public law and human rights, and is increasingly sought after for her advocacy skills in a broad range of commercial, regulatory and enforcement matters, particularly in the appellate Courts. In 2019-20 Marie won both the Chambers & Partners Competition Silk of the Year and the Legal 500 EU and Competition Silk of the Year awards and was also one of 12 barristers to be named as one of The Lawyer’s Hot 100 2020.  Marie is also Star Rated for competition law in the Chambers & Partners directory. Since 2015 Marie has been Standing Counsel to the Competition and Markets Authority, representing the CMA in its major litigation in the courts. Between 2016 and 2018 Marie was Chair of the Bar European Group.

Marie Demetriou KC is widely recognised as a leading advocate in the fields of competition law, EU law, public law and human rights. In 2019-20 Marie won both the Chambers & Partners Competition Silk of the Year and the Legal 500 EU and Competition Silk of the Year awards and was also one of 12 barristers to be named as one of The Lawyer’s Hot 100 2020.  Marie is also Star Rated for competition law in the Chambers & Partners directory. Since 2015 Marie has been Standing Counsel to the Competition and Markets Authority, representing the CMA in its major litigation in the courts. Between 2016 and 2018 Marie was Chair of the Bar European Group.

Some current and recent highlights of Marie’s practice (spanning competition law, EU law and public law) are:

  • Representing Mr Micula in the Supreme Court in his application to enforce his ICSID arbitration award in circumstances where the European Commission has determined that enforcement would amount to state aid (Micula v Romania).
  • Acting for the CMA in the Court of Appeal in Ping v CMA, concerning the ambit of infringements of competition law ‘by object’ and bans on internet sales.
  • Representing HMT against BT in the Court of Appeal in a judicial review concerning reforms to public service pensions.
  • Representing Mr Merricks successfully in the Court of Appeal in the UK’s first and largest collective competition action (Merricks v Mastercard); a hearing before the Supreme Court is pending.
  • Representing the CMA in the ‘pay for delay’ litigation both before the CAT (GlaxoSmithKline v CMA [2018] CAT 4, and in the reference made by the CAT to the CJEU.
  • Acting for three large claimant groups in the Trucks Cartel Damages litigation.
  • Acting for a number of claimants in the first Foreign Exchange damages claim pending before the High Court.
  • Acting for defendants in the Power Cables damages claim due to be heard at the end of 2020.
  • Successfully acting for Monarch Airlines in the Court of Appeal in relation to the allocation of valuable landing slots after Monarch was placed into administration (R(Monarch Airlines Limited) v Airport Coordination Limited [2017] EWCA Civ 1892).
  • Representing Apple in its competition law/ FRAND claim against Qualcomm arising out of the licensing by Qualcomm of its chips used for Apple devices.
  • Successfully challenging the Government’s nationwide policy to deport EU nationals found sleeping rough (Gureckis and others v Secretary of State for the Home Department [2017] EWHC 3298 (Admin).
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  • Competition M

    Marie is Star Rated by Chambers & Partners in competition law.  She is instructed in many of the leading competition cases in the CAT and the courts.  Since 2015, Marie has been Standing Counsel to the Competition and Markets Authority.  As well as acting for the CMA in its major litigation and investigations (including the ‘pay for delay’ appeals, Eurotunnel/SeaFrance in the Supreme Court, Ping v CMA, a number of mergers appeals and market investigations), Marie acts for a large variety of private clients in damages claims (including those arising from the decisions in Trucks, FX, Roll-on Roll-off Ferries, Gas Insulated Switchgear, Power Cables, Envelopes, Ball Bearings, Cathode Ray Tubes, Mobile Phone Batteries) as well as in stand-alone competition actions and FRAND claims.  In 2019, Marie was awarded both Competition Law Silk of the Year by Chambers & Partners and EU and Competition Silk of the year by Legal 500. 

    Notable cases include:

    • Ping v Competition and Markets Authority, Court of Appeal, nature of restriction of competition by object/ lawfulness of internet sales ban.  Represented CMA.
    • Merricks v Mastercard, [2018] EWCA Civ 2527, [2019] EWCA Civ 674, Supreme Court hearing pending. Acting for UK consumers in large collective action; instructed by Quinn Emanuel.
    • Veolia and others v Fiat Chrysler and others (acting for claimants in relation to Trucks cartel, instructed by Hausfeld).
    • Allianz Global v Barclays Bank and other (FX), acting for claimants, instructed by Quinn Emanuel.
    • National Grid v ABB and others, High Court, acting for NKT, instructed by Addleshaw Goddard.
    • Société Coopérative de Production SeaFrance v CMA [2015] UKSC 75, successfully represented CMA in appeal against meger decision.
    • GlaxoSmithKline v CMA (“pay for delay”) [2018] CAT 4, reference before CJEU pending.  Represented CMA.
    • Apple v Qualcomm (Article 102 / FRAND claim in relation to licensing by Qualcomm of its chipsets used in Apple devices; judgment on jurisdiction [2018] EWHC 1188 (Pat).  Representing Apple, instructed by Boies Schiller LLP.
    • Iiyama v Samsung and others [2018] EWCA Civ 220.  Acted for Philips, instructed by Slaughter and May.
    • Daimler v MOL and others, (Ro-Ro), [2019] EWHC 3197 (Comm), acting for NYK, instructed by Steptoe and Johnson.
    • Sky/ Fox; acted for CMA in investigation into public interest in permitting Sky Fox merger.
    • Federal Deposit Insurance Corporation v Barclays Bank Plc (large competition damages claim arising out of LIBOR manipulation; acting for claimant, instructed by Quinn Emanuel.
    • National Grid and Scottish Power v ABB and others; acting for NKT, instructed by Addleshaw Goddard in large cartel damages claims arising from the Power Cables Cartel.
    • Vattenfall v ABB and others; acting for NKT, instructed by Addleshaw Goddard; further claim arising from Power Cables Cartel.
    • International Exchange Inc v Competition and Markets Authority [2017] CAT 6; successfully represented CMA in ICE’s appeal against CMA decision requiring unwinding of merger.
    • Microsoft v Sony, Samsung and LG Chem [2017] EWHC 374 (Ch); acted for LG Chem, instructed by Steptoe and Johnson; successfully challenged the jurisdiction of the English court to determine this large cartel damages claim.
    • CMA market investigation into retail banking; acted for CMA.
    • CMA market investigation into energy; acted for CMA.
    • Deutsche Bahn v Morgan Crucible [2014] UKSC 24; (successfully persuaded Supreme Court to strike out claim against Morgan crucible on the ground it was time barred; instructed by Clifford Chance).
    • National Grid v ABB and others [2009] EWHC 1326 (Ch), (cartel damages claim arising from Commission decision in gas-insulated switchgear
    • Cooper Tyre and Rubber Co v Bayer and others (Commercial Court; cartel damages claim)
    • Air Cargo, acting for SAS
    • Crest Nicholson Plc v OFT [2011] CAT 10 (appeal against penalty; bid-rigging in construction industry)
    • BSkyB v Competition Commission; Virgin Media v Competition Commission [2010] EWCA Civ 2 (Court of Appeal; application of media plurality provisions in Enterprise Act; Sky's acquisition of shareholding in ITV)
    • Sky v Ofcom; FA Premier League v Ofcom (CAT; Pay TV; challenge to Ofcom's decision to require Sky to provide its two main sports channels to its competitors)
    • Barclays Bank Plc v Competition Commission (PPI) [2009] CAT 27 (Challenge to Competition Commission's Report on payment protection insurance)
    • Vodafone, Orange, O2 and T-Mobile v Ofcom [2010] EWCA Civ 391 (Court of Appeal; respective jurisdictions of the CAT and the OFT in appeals under the Communications Act)
    • BT v Ofcom [2009] CAT 11 (mobile call termination)
    • Orange Personal Communications Services Ltd v Ofcom [2007] CAT 36 (Ofcom's dispute resolution powers under the Communications Act 2003)
    • H3G v Ofcom [2008] CAT 11 (significant market power in the market for wholesale mobile voice call termination)
    • Vodafone v Ofcom [2008] CAT 22 (mobile number portability)
    • BT v Ofcom (0845/0870 numbers)
    • Crehan v Inntrepreneur Pub Company [2006] UKHL 38 (House of Lords; damages action; status of Commission decisions in national courts)
    • Hutchison 3G UK Ltd v O2, Orange, T-Mobile and Vodafone [2008] EWHC 55 Comm (Commercial Court; pre-action disclosure; Article 81 EC)
    • Argos and Littlewoods v OFT [2006] EWCA Civ 1318 (Court of Appeal; price-fixing)
    • AAH Pharmaceuticals v Pfizer and Unichem [2007] EWHC 565 (High Court; interim injunction; Articles 81 and 82; distribution of pharmaceuticals)
    • OFT's Market Enquiry into distribution of pharmaceuticals. Represented the British Association of Pharmaceutical Wholesalers.
    • Trouw UK Limited v Nippon Soda and Mitsui (Commercial Court; cartel damages claim
    • Independent Schools - price-fixing
  • EU law M

    Marie has acted in many high-profile and diverse EU law cases before the English and European Courts, including acting in challenges to the 2nd Tobacco Products Directive and the UK plain packaging legislation; the Micula ligitation raising the interrelationship between ICSIC arbitration awards and EU law;  aviation cases (Monarch Airlines, Tui Travel and IATA); a range of pharmaceutical cases (including PTC Therapeutics, pay for delay litigation, GMP-Orphan in relation to orphan drugs); asylum and human rights claims (NS, El Kott) and sanctions cases (PMOI, Bank Saderat).  Marie was a référendaire to Judge Edward at the ECJ, Chair of the Bar European Group between 2016-2018; Visiting Fellow at the Centre for European Law, King’s College, London and a Trustee of the Slynn Foundation.  Notable cases include:

    • R (Monarch Airlines) v Airport Coordinator [2017] EWCA Civ 1892.
    • Micula v Government of Romania [2017] EWHC 31, judgment of CA pending.  Acting for Claimant, instructed by White and Case in enforcement of ICSID Award in circumstances where Commission has determined payment would constitute state aid.
    • Apple v Qualcomm (Article 102 / FRAND claim in relation to licensing by Qualcomm of its chipsets used in Apple devices; judgment on jurisdiction [2018] EWHC 1188 (Pat).  Representing Apple, instructed by Boies Schiller LLP.
    • R (Gureckis and others) v Secretary of State for the Home Department [2017] EWHC 3298 (Admin).  Acted for claimants, instructed by Lambeth Law Centre, in successful challenge to Government policy of deporting EEA nationals found sleeping rough.
    • Case C-267/16 Buhagiar v Ministry of Justice (CJEU; reference from Gibraltar courts re scope of application of the Treaty to Gibraltar).
    • Case T-718/15 PTC Therapeutics v European Medicines Agency; acting for claimant, instructed by Covington and Burling, confidentiality of pharmaceutical information).
    • Case T-733/17 GMP Orphan SA v European Commission (challenge to failure to confer orphan drug designation).
    • Case T-433/15 Bank Saderat v Council and Commission, damages claim on behalf of claimant bank seeking damages for unlawful sanctions imposed by Council, instructed by Stephenson Harwood.
    • Case C-547/14 Philip Morris v Secretary of State for Health, CJEU judgment of 4 May 2016; acted for Philip Morris, instructed by Skadden Arps in challenge to 2nd Tobacco Products Directive.
    • R (British American Tobacco) v Secretary of State for Health [2016] EWHC 1169 (Admin); acted for Philip Morris, instructed by Skadden Arps in challenge to UK plain packaging regulations.
    • ZAT v Secretary of State for Home Department [2016] EWCA Civ 810; acted for UNHCR in appeal concerning rights of unaccompanied child asylum seekers.
    • MSM (Somalia) v Secretary of State for Home Department [2016] EWCA Civ 715; acted for UNHCR in appeal concerning interpretation of Qualification Directive.
    • Mirga v Secretary of State for Work and Pensions [2016] UKSC 1; acted for AIRE Centre in Supreme Court appeal concerning rights to social security of migrant workers.
    • R (W,X,Y and Z) v Secretary of State for Health [2015] EWCA Civ 1034; acted for Secretary of State for Health in successfully resisting challenging to NHS data sharing arrangements.
    • Case C-411/10 NS (CJEU; asylum; effect of EU Charter of Fundamental Rights)
    • Case C-364/11 El Kott (CJEU; rights of Palestinian refugees)
    • EM(Eritrea) v Secretary of State for Home Department [2014] UKSC 12; acted for UNHCR in Supreme Court Appeal relating to Dublin Regulation.
    • Joined Cases C-199/12 and C-201/12 X, Y and Z (CJEU, asylum, sexual orientation)
    • Joined Cases C-403/08 and C-429/08 QC Leisure and others v FA Premier League (CJEU; cross-border broadcasting; intellectual property)
    • Joined Cases C-581/10 and C-629/10 TUI Travel and others v CAA (CJEU; obligations of airlines in event of delays to flights)
    • Case C-281/09 Commission v Spain (CJEU; television advertisting)
    • Case C-512/08 Commission v France (CJEU; free movement, cross-border healthcare)
    • Case C-27/09P France v People's Mojahedin of Iran (CJEU, asset freezing)
    • Case C-420/07 Apostolides v Orams (CJEU; status of the occupied area of Cyprus; conflict of laws)
    • Case T-284/08 People's Mojahedin of Iran (General Court; list designating terrorist organisations; asset freezing; human rights)
    • Case C-336/08 Reinke (CJEU, cross-border healthcare; social security)
    • Case C-142/09 Lahousse (CJEU; transport; free movement)
    • Case C-438/05 Viking Line v International Transport Workers' Federation and Finnish Seamen's Union (CJEU, free movement; right to strike)
    • Case C-344/04 R(IATA) v Secretary of State for Transport [2006] ECR I-403 (CJEU; passenger compensation for cancelled and delayed flights)
    • Case C-506/04 Wilson [2006] ECR I-8613 (CJEU, freedom of establishment for lawyers)
    • Timbrell v Secretary of State for Work and Pensions [2010] EWCA Civ 71 (Court of Appeal; application of Equal Treatment Directive to transsexuals)
    • Interfact Ltd v Liverpool City Council; R v Rainbird and Budimir [2010] EWCA Crim 148 (Court of Appeal; consequence of failure to notify legislation under Technical Standards Directive)
    • Oracle America v M-Tech Data Ltd [2010] EWCA Civ 997 (Court of Appeal; EU trade mark/ free movement)
    • R (Countryside Alliance and others) v HM Attorney General [2007] UKHL 52, [2007] 3 WLR 922 (House of Lords; Challenge to the Hunting Act)
    • REPIC Ltd v Secretary of State for Business, Enterprise and Regulatory Reform [2009] EWHC 2015 (Admin) (EU waste legislation)
    • Liu and others v Secretary of State for the Home Department [2007] EWCA Civ; and W(China) and X(China) v Secretary of State for the Home Department [2006] EWCA Civ 1494 (both Court of Appeal; EU citizenship)
  • Public Law M

    Marie is recommended in the principal directories as a leading advocate in public law and human rights. Prior to taking Silk she was a member of the Attorney General’s ‘A’ Panel of Counsel. She acts for both claimant, defendants and NGOs in public law and human rights cases before the English Courts, the EU Courts and the European Court of Human Rights. Recent / current cases include acting for the Independent Monitoring Authority in the Supreme Court and the Court of Appeal on two cases concerning the scope of the Withdrawal Agreement; acting for the Aire Centre in the Court of Appeal concerning the rights of EU citizens; acting for the Government in the Archie Battersbee case; acting for British Sugar in relation to whether a trade tariff falls within the scope of the state aid provisions of the Northern Ireland Protocol; acting for Stagecoach in a judicial review of the bus franchising arrangements in Manchester; representing UNHCR in several asylum cases before the CJEU; representing the CMA before the Court of Appeal in relation to the extraterritorial reach of its investigatory powers; acting for Transport for London in successfully resisting the challenge to the extension of the congestion charging scheme to minicabs.

    Notable cases include:

    • AT v Secretary of State for Work and Pensions (Court of Appeal, pending.  Represented the IMA on the question whether the EU Charter of Fundamental Rights continues to apply to EU citizens in the UK via the Withdrawal Agreement);
    • The King (Volkswagen) v Competition and Markets Authority (Court of Appeal, pending.  Representing the Competition and Markets Authority on the extraterritorial reach of the CMA’s investigatory powers);
    • R (British Sugar Plc) v Secretary of State for International Trade [2022] EWHC 393 (Admin) (represented the Claimant; first case on meaning and scope of the Northern Ireland Protocol).
    • Archie Battersbee (acted for the Secretary of State for Health and Social Care, intervening before the Supreme Court in relation to the effect of a request to the UN Committee on the Rights of Persons with Disabilities to a decision to case providing life-preserving treatment).
    • Fratila v Secretary of State for Work and Pensions [2021] UKSC 53 (represented the IMA on the compatibility with EU law of provisions governing the entitlement to benefits of EU citizens);
    • Greater Manchester Buses v Greater Manchester Combined Authority [2022] EWHC 506 (Admin) (represented the Claimant in challenge to bus franchising arrangements in Manchester).
    • Case C-349/20 NB v Secretary of State for the Home Department, 3 March 2022 (acted for UNHCR in this reference to the CJEU which addressed the test by which stateless persons of Palestinian origin should be granted refugee status).
    • Facebook v Competition and Markets Authority [2021] EWCA Civ 701 (acted for the CMA in resisting a challenge to the procedure it followed in investigating Facebook’s merger with Giphy).
    • Independent Workers Union of Great Britain v Mayor London and Transport for London [2020] EWCA Civ 1046 (acted for the Respondents in successfully resisting a challenge on human rights grounds to the extension of the congestion charging scheme to minicabs).
    • R (British Telecommunications Plc) v HM Treasury [2020] EWCA Civ 1 (represented HM Treasury in resisting challenge to its decision to implement full indexation of the guaranteed minimum pension payable to public service pensioners).
    • R (Advanz Pharma) v Competition and Markets Authority [2019] EWHC 1605 (Admin) (represented the CMA in resisting a challenge to its refusal to stay its investigation into the alleged excessive pricing of Liothyronine).
    • Eurotunnel v Secretary of State for Transport (acted for Brittany Ferries, intervening, in Eurotunnel’s challenge to contracts awarded by the Government to Brittany Ferries and others in order to provide additional freight capacity between the UK and continental Europe in the context of Brexit).
    • R (Monarch Airlines Limited) v Airport Coordination Limited [2017] EWCA Civ 1892 (successfully challenged ACL’s decision denying Monarch its valuable landing slots on the ground that it had been placed into administration).
    • R (Gureckis and others) v Secretary of State for the Home Department [2017] EWHC 3298 (Admin). Acted for claimants, instructed by Lambeth Law Centre, in successful challenge to Government policy of deporting EEA nationals found sleeping rough.
    • R (British American Tobacco) v Secretary of State for Health [2016] EWHC 1169 (Admin); acted for Philip Morris, instructed by Skadden Arps in challenge to UK plain packaging regulations.
    • R (State of Guernsey) v Secretary of State for Environment [2016] EWHC 1847 (Admin); acted for States of Guernsey in dispute with UK Government in relation to fishing rights.
    • R (Napp Pharmaceuticals) v Secretary of State for Health [2016] EWHC 1982 (Admin); acted for claimant in challenge to decision of MHRA.
    • R (W,X,Y and Z) v Secretary of State for Health [2015] EWCA Civ 1034; acted for Secretary of State for Health in successfully resisting challenging to NHS data sharing arrangements.
    • ZAT v Secretary of State for Home Department [2016] EWCA Civ 810; acted for UNHCR in appeal concerning rights of unaccompanied child asylum seekers.
    • MSM (Somalia) v Secretary of State for Home Department [2016] EWCA Civ 715; acted for UNHCR in appeal concerning interpretation of Qualification Directive.
    • R (Barda) v Mayor of London [2015] EWHC 3584 (Admin); acted for claimant in challenge to Mayor’s decision to ban protests outside Parliament.
    • EM (Eritrea) v Secretary of State for Home Department [2014] UKSC 12; acted for UNHCR in Supreme Court Appeal relating to Dublin Regulation.
    • AD v Home Office [2015] EWHC 663 (QB); acted for refugee in damages claim against Home Office.
    • R (Cushnie) v Secretary of State for Health [2014] EWHC 3626 (Admin); represented Secretary of State in challenge to NHS (overseas) regulations.
    • Obrey v Secretary of State for Work and Pensions [2013] EWCA Civ 1584; acted for Secretary of State in appeal raising approach at appeal stage to proportionality assessments made by specialist tribunals.
    • Case C-411/10 NS (ECJ; effect of EU Charter of Fundamental Rights)
    • Case C-364/11 El Kott (ECJ; rights of Palestinian refugees)
    • R (Eventech) v TFL (Admin Court; Addison Lee's challenge to TFL's bus lanes policy)
    • Timbrell v Secretary of State for Work and Pensions [2010] EWCA Civ 71 (Court of Appeal; application of Equal Treatment Directive to transsexuals)
    • Interfact Ltd v Liverpool City Council; R v Rainbird and Budimir [2010] EWCA Crim 148 (Court of Appeal; consequence of failure to notify legislation under Technical Standards Directive)
    • R (EM and others) v Secretary of State for Work and Pensions [2010] EWCA Civ 18 (Court of Appeal; Article 14 ECHR; entitlement of psychiatric patients to social security benefits)
    • Case T-284/08 People's Mojahedin of Iran, judgment of 4 December 2008 (General Court; list designating terrorist organisations; asset freezing; human rights)
    • R (Countryside Alliance and others) v HM Attorney General [2007] UKHL 52, [2007] 3 WLR 922 (House of Lords; challenge to the Hunting Act)
    • R (Crest Nicholson) v OFT [2009] EWHC 1875 (Admin) (Challenge to OFT's settlement procedure)
    • AL v Human Fertilisation and Embryology Authority and Secretary of State for Health [2008] EWHC 2149 (Fam) (Article 8 ECHR; fertility treatment; consent requirements)
    • Mirga and Samin v Secretary of State for Work and Pensions [2016] UKSC 1; acted for Aire Centre intervening in Supreme Court appeal relating to social security rights of EU migrants.
    • Liu and others v Secretary of State for the Home Department [2007] EWCA Civ; and W(China) and X(China) v Secretary of State for the Home Department [2006] EWCA Civ 1494 (both Court of Appeal; EU citizenship)
    • R (Crouch) v South Birmingham Primary Care Trust and Secretary of State for Health [2008] EWHC 605 (Admin) (NHS arrangements for dentists)
    • R (Compassion in World Farming) v DEFRA [2004] EWCA Civ 1009 (livestock protection legislation)
    • Campbell v Secretary of State for Work and Pensions [2004] 3 All ER 387 (Court of Appeal; Article 9 ECHR)
    • Former King of Greece v Greece 33 EHRR 21 (European Court of Human Rights; Article 1 of Protocol No 1)
    • Hashman and Harrup v UK 30 EHRR 241 (European Court of Human Rights)
  • Publications M
    • References to the European Court (2nd ed, Sweet & Maxwell), Co-author with David Anderson KC.
    • Sports Law (Hart Publishing), Co-author with Michael Beloff KC and Tim Kerr KC (2nd ed, October 2012)
    • Contributor to Judicial Review, Principles and Procedure (OUP, 2013)
    • Contributor to Competition Litigation (OUP)
    • Numerous articles in legal journals
    • Member of the Editorial Boards of World Competition (Kluwer) and International Sports Law Review (Sweet and Maxwell).
  • Qualifications M

    BA, BCL (1st Class) (Oxon)

  • Directory Quotes M
    • "Marie is just outstanding. She is so talented and is such a fantastic and clear thinker." (Chambers & Partners 2025)
    • "She is an amazing advocate." (Chambers & Partners 2025)
    • "Marie is amazing. She is super clever and an amazing advocate." (Chambers & Partners 2025)
    • "She's great to work with and very experienced. She is systematic, structured and very approachable." (Chambers & Partners 2025)
    • "Marie is absolutely brilliant, a really incomparable courtroom advocate." (Chambers & Partners 2025)
    • "She is just outstanding. She is so talented and such a fantastic and clear thinker." (Chambers & Partners 2025)
    • "She is outstanding at cross-examination, very well prepared and super-smart." (Chambers & Partners 2025)
    • "Marie has incredible knowledge of the law. She delivers very clear and persuasive submissions." (Chambers & Partners 2025)
    • "Marie Demetriou KC is very calm and has an authoritative presence in hearings." (Chambers & Partners 2025)
    • "Marie Demetriou KC is very smart and is an impressive performer in court." (Chambers & Partners 2025)
    • "She is very smart and an impressive performer in court." (Chambers & Partners 2025)
    • "A silk with excellent judgement, who provides clear and concise advice." (Legal 500 2025)
    • "Marie is unique amongst aviation silks in bringing together commercial experience and acuity with regulatory and public law expertise. She is also among the best advocates at the Bar today, full stop." (Legal 500 2025)
    • "Marie is a total star in several areas of practice not just competition law - which is the real hallmark of a first-rate barrister. She has a sixth sense for the winning point and has unparalleled advocacy skills to then execute it. She is first choice in the most difficult and cutting edge matters. Peerless." (Legal 500 2025)
    • "Marie really is the best advocate at the Bar in EU and competition matters. Excellent judgement, extremely tight legal analysis and an extremely persuasive advocate." (Legal 500 2025)
    • "Marie combines encyclopaedic expertise with an ability to convey complex concepts in the clearest possible terms. As a result, her advocacy, and advice to clients, is always crystal clear and her logic infallible." (Legal 500 2025)
    • "Marie is very knowledgeable on EU law and has been able to provide clear and practical advice on how that applies to the interpretation and application of the Withdrawal Agreement." (Chambers & Partners 2024)
    • "Marie is one of the absolute top silks in this field." (Chambers & Partners 2024)
    • "Marie can be a very effective advocate and is very client-friendly." (Chambers & Partners 2024)
    • "Marie is simply straight out of the top drawer, and it is hard to think of a competition silk more at the top of their game right now. Despite her busy practice, with many marquee instructions, when she is focused on your case there is no one better to have in your corner, and on her feet she is simply excellent, commanding the respect of the judges she appears before as well as the listening ear of the client." (Chambers & Partners 2024)
    • "Marie is first class in every respect. She could not be nicer or easier to work with, but she combines that with the most effective advocacy and razor-sharp strategic skill." (Chambers & Partners 2024)
    • "She is operating at the very pinnacle of competition litigation." (Chambers & Partners 2024)
    • "She is one of the pre-eminent barristers of the competition Bar." (Chambers & Partners 2024)
    • "She is brilliant and one of the best I have worked with. She is super bright and on top of the detail and strategy." (Chambers & Partners 2024)
    • "She is very sharp and fast on her feet." (Chambers & Partners 2024)
    • "She is incredibly effective and she is clear and precise." (Chambers & Partners 2024)
    • "Her advocacy really marks her out; she is conscious of the strongest part in the case and her advocacy wins out every time." (Chambers & Partners 2024)
    • "An absolutely first-class operator. She has a brilliant razor-sharp mind when extracting the key points." (Chambers & Partners 2024)
    • "All-round excellent." (Chambers & Partners 2024)
    • "Marie is measured and always has an interesting take on a case." (Chambers & Partners 2024)
    • "She has excellent judgement." (Legal 500 2024)
    • "One of the absolute stars of the competition Bar and seen as one of the best of the best for very good reason. Brilliant legal and tactic analysis, only takes good points, cuts through the noise and nonsense and so everyone listens when Marie makes a point in court." (Legal 500 2024)
    • "Even under pressure, Marie manages to present calm, well reasoned and clear arguments." (Legal 500 2024)
    • "A formidable and cogent advocate." (Legal 500 2024)
    • "Marie is strong at giving evidence on complicated issues concerning human rights and EU law." "She understands the importance of the issues involved for the client, and takes a very sophisticated approach in order to address them." (Chambers & Partners 2023)
    • "She is a very impressive advocate." "Marie is a fantastic drafter, who is able to get an argument across very clearly and concisely in a very persuasive form. She is incredibly thoughtful and articulate when dealing with courts, clients and regulators." (Chambers & Partners 2023)
    • "She is really authoritative and insightful and an excellent advocate." "Her advocacy is measured and fair and she is down to earth. She is rightly trusted by judges." (Chambers & Partners 2023)
    • "She was absolutely phenomenal as an advocate. Ridiculously impressive, even when under a lot of pressure." (Chambers & Partners 2023)
    • "She's always very helpful, is a fantastic drafter and is able to get the argument across very clearly, concisely and in very persuasive form." "She is incredibly thoughtful and articulate when dealing with courts, clients and regulators." "She has really smooth advocacy, a very silky style. She charms the judges but is not a pushover. She is an iron fist in a velvet glove." (Chambers & Partners 2023)
    • "Unrivalled knowledge of the public law aspects of Aviation regulation, slots trading and insolvency matters." (Legal 500 2023)
    • "Tremendous advocacy. Really persuasive and engaging, and makes everything sound very simple." (Legal 500 2023)
    • "Very thoughtful and considered approach." (Legal 500 2023)
    • "Marie is a brilliant courtroom advocate, particularly strong in appellate court." (Legal 500 2023)
    • "Marie is outstanding and a star in the competition sky. Her advocacy makes everything sound extremely simple and straightforward." (Legal 500 2023)
    • "She is a fantastic oral advocate – she has a calm, measured style which is very persuasive." "She is brilliant to work with and so clear in what she says; she comes across very well in court." "Has an incredibly incisive mind and spots the issues."  (Chambers & Partners 2022)
    • "It was Marie's voice of clear and calm that won the case." "Marie is the standout because she is extremely clever and has an excellent advocacy style; she is also measured, respected and down to earth." (Chambers & Partners 2022)
    • "Marie is a really excellent EU lawyer who is also involved in interesting civil liberties cases." (Chambers & Partners 2022)
    • "She's first class and very able. Her background in competition law allows her to operate across a wide field in aviation." "She's very thoughtful and precise." (Chambers & Partners 2022)
    • "She is a great advocate with extraordinary experience in the EU and domestic courts." "She has an engaging manner as an advocate as well as providing clear and direct advice for clients." (Chambers & Partners 2022)
    • "Marie is absolutely my top choice in this area. A subject matter specialist and a considered and effective advocate. She is good at delivering difficult messages."  (Legal 500 2022)
    • "A forceful and persuasive advocate able to fend off fierce opposition and persuade a sceptical court of difficult points." (Legal 500 2022)
    • "Super clever, excellent advocate, commercial and user-friendly." (Legal 500 2022)
    • "A forceful and persuasive advocate able to fend off fierce opposition and persuade a sceptical court of difficult points." (Legal 500 2022)
    • "Marie is an amazing advocate: succinct, precise, and judges are very receptive to her." "She makes points very clearly and is easy to understand." "She is so talented and just a joy to work with." "Marie is super clever and a fantastic advocate." (Chambers & Partners 2021)
    • "The most concise lawyer I've come across - every word counts. She wins so often." "A pre-eminent EU lawyer and a very convincing public law advocate." (Chambers & Partners 2021)
    • "She has phenomenal experience in the European courts and is really amazing." "Marie's advocacy is very clear, sensible and clever, and she knows how to get results." (Chambers & Partners 2021)
    • "Excellent in the courtroom and very strong on written work." (Chambers & Partners 2021)
    • "She's hard-working and clever, a very good advocate who can turn her hand to just about anything." (Chambers & Partners 2021)
    • "Excellent on EU sanctions law, responsive and approachable. A great combination." (Legal 500 2021)
    • "Her submissions are perfectly succinct and have more impact with judges than most." (Legal 500 2021)
    • "Absolutely one of the top EU law silks around – excellent in court and always has a real grasp of the issues. Astute in her analysis, clear and compelling in her advocacy, we knew our case could not be in better hands." (Legal 500 2021)
    • "A forceful and persuasive advocate able to fend off fierce opposition and persuade a sceptical court of difficult points." (Legal 500 2021)
    • Marie Demetriou KC is “highly rated” by clients who have “complete confidence instructing her on medicine-related regulatory disputes”. (Who's Who Legal - UK Bar: Competition 2020)
    • "Commands great respect for her expertise in public law cases involving provisions of EU law. She also handles cases concerning human rights, data protection, immigration and asylum, and PIL. She receives instructions from claimants, regulators, government departments and other interested parties." "Incredibly creative and very effective indeed on her feet."  (Chambers & Partners 2020)
    • "An esteemed silk demonstrating core strength in areas such as political protest, immigration and torture. She is typically seen assisting claimants and intervenors, regularly representing the UNHCR in important asylum rights cases." "A really good advocate, great on her feet and incredibly clever; her points are backed by a lot of intellectual force." (Chambers & Partners 2020)
    • "She is a very impressive advocate and her presentation is very clear." "She is able to quickly get up to speed in a very technical area" and is "willing to listen and take on ideas." (Chambers & Partners 2020)
    • "Enters the list of star competition law silks owing to consistently superb feedback from diverse sources. She is standing counsel to the CMA and has experience in key cases that test the law around restrictions on online sales. She also advises on both sides of cartel damages claims, and has appeared on behalf of proposed class representatives for claimant groups." "Incredibly resilient and doesn't let points go. She can change the shape of a hearing at will." "Marie is an amazingly calm presence, who cuts through issues and offers incisive, high-quality advice." "She is a team player who gets the best out of everyone on a case." (Chambers & Partners UK & Global 2020)
    • "Totally on top of European human rights case law, providing strategic litigation advice." (Legal 500 2020)
    • "She has great authority with the judge and other counsel." (Legal 500 2020)
    • "Formidable counsel to have on your side, even more formidable on the other side." (Legal 500 2020)
    • Marie Demetriou KC comes highly recommend by peers as “a tremendously impressive practitioner and very strong individual”. Her experience includes competition damages claims for some of the world’s largest technology and financial services companies. (Who's Who Legal - UK Bar: Competition)
    • Marie Demetriou KC is praised extensively by peers this year as “simply a class act” who is “is extremely highly regarded at the bar”. Her practice specialises in competition, public and EU law. (Who's Who Legal - UK Bar: Telecoms 2019)
    • "She is absolutely excellent. She was all over the detail, and very friendly and easy to work with." "Careful and rigorous." (Chambers & Partners 2019)
    • "She has an incredible ability to read judges and understand exactly what they need." "She is very responsive, approachable and gives very pragmatic advice. She is very empathetic with vulnerable clients." (Chambers & Partners 2019)
    • "She offers a really powerful strategic view on a case, providing a good overview of the key issues and producing outstanding advocacy." (Chambers & Partners UK & Global 2019)
    • "She is clearly at the top of her game in European law, offering an outstanding clarity of thought and understanding of the commercial points." (Chambers & Partners 2019)
    • "She was brilliant on an urgent judicial review and delivered a fantastic result for the client." (Legal 500 2018-19)
    • "Formidable advocate and fantastic strategist." (Legal 500 2018-19)
    • "Timely in responding to questions, approachable and easy to work with, constructive, and has a good sense of judgement, including in advocacy." (Legal 500 2018-19)
    • "‘Manages to make the implausible sound plausible, using a very calm measured style." (Legal 500 2018-19)
    • Marie Demetriou KC receives plaudits for her expertise in public law competition cases and her considerable experience working with regulators. She is praised for her “excellent judgement” and is recognised as “one of the leaders in the competition space”. (Who's Who Legal - UK Bar: Competition 2018)
    • "Incredibly responsive and very, very collaborative. Also, the quality of her oral submissions is fantastic. He is very good at drilling into the crux of an issue and presenting it in a way which is really helpful. She is user-friendly and brings a lot of clarity to murky cases." (Chambers & Partners 2018)
    • "Very responsive and very approachable, Marie is quick to get to grips with complex facts. She gives very clear, pragmatic advice and is excellent on her feet." (Chambers & Partners 2018)
    • "She is an exceptionally good barrister to have on the team, with the ability to get on top of the detail quickly and see things from the client's perspective." (Chambers & Partners 2018)
    • "She is a calm and assured performer who gets her points over well." (Chambers & Partners 2018)
    • "Clearly intelligent, with the ability to reduce complex issues to simple ones for the court." (Legal 500 2017)
    • "She has an effective manner in court and is one of her clients’ favourite advocates." (Legal 500 2017)
    • "A calm and assured performer, who gets her points across well." (Legal 500 2017)
    • "Marie Demetriou KC is distinguished by her ability to “cut through complexity” and for her “excellent judgement”. She is standing counsel to the CMA, as well as a popular counsel to commercial clients and other public bodies in complex competition law actions." (Who's Who Legal - UK Bar: Competition 2017)
    • "Marie Demetriou KC is highlighted for her expertise in this area as a “top-tier” competition, EU and public law barrister." (Who's Who Legal - UK Bar: Telecoms 2017)
    • "She's jolly good and does a lot of telecoms work." "A very able advocate." (Chambers & Partners 2017)
    • "Very responsive and very approachable, she is quick to get to grips with the complex facts of a case and gives very clear and pragmatic advice." (Chambers & Partners 2017)
    • "She's gently persuasive and one of the most charming advocates on the stage." "She has a wonderfully conversational advocacy style which anyone can follow." (Chambers & Partners 2017)
    • "Really strong on her feet. She has real weight and presence in court. She can hold her own against unpleasant and aggressive opponents and is also really good with the client. A pleasure to deal with." "A deep understanding and analytically bright. She is utterly charming and quickly establishes a rapport with both judges and clients." (Chambers & Partners 2017)
    • "She carries immense authority in the field of competition litigation and is well known and respected by competition law practitioners. It is very good to be seen having her fighting on your side." (Chambers & Partners 2017)
    • "Marie Demetriou KC is internationally nominated for her practice which comprises significant experience acting for clients in the pharmaceutical and telecommunications sector." (Who's Who Legal - Competition 2017)
    • "A formidable advocate and fantastic strategist." (Legal 500 2016)
    • "Enormously impressive and pitch-perfect in difficult hearings." (Legal 500 2016)
    • "She is effortlessly cool - she doesn't have any nerves or ever get stressed." (Chambers & Partners 2016) 
    • "An extremely personable and client-friendly silk with a stellar reputation for cases which have an EU law aspect." (Chambers & Partners 2016) 
    • "She is outstanding at making the complex simple and really cutting through to the key issues." (Chambers & Partners 2016) 
    • "She is hugely clever and a very logical thinker who is very easy to work with." "She is very legally astute and knowledgeable, particularly in EU and human rights law, where she adds a lot of value." (Chambers & Partners 2015) 
    • "She is excellent and extremely easy to work with. She is very approachable, and pragmatic in coming to a solution that will make everybody happy." "Very easy-going and relaxed, but also very efficient in the way she goes about her work, and very sharp when it comes to European law." (Chambers & Partners 2015)
    • "Absolutely outstanding." "She is very easy to work with and very responsive." (Chambers & Partners 2015)
    • “Earns praise from clients for her proactive approach to client service. She is particularly appreciated for her ability to explain complex issues in a concise yet effective manner.” (Chambers & Partners 2015) 
    • "I found her EU legal expertise to be second to none." "She was extraordinarily impressive and responsive. She has a high degree of commitment and flexibility, meaning she is ready to comply with tight deadlines." (Chambers & Partners 2015) 
    • "She's smart and user-friendly, and performs well on telecoms competition matters." (Chambers & Partners 2015) 
    • "Fiercely bright and strategic." (The Legal 500 2014)
    • "Instructing solicitors are gushing in their praise of Marie Demetriou. Fantastically bright, and a pleasure to work with," she offers "sound, pithy advice, is a team player and is someone clients trust and like." (Chambers UK 2012)
    • "Marie Demetriou is "a highly intellectual barrister who is the most pragmatic of performers." Solicitors favour her as "she takes absolutely everything into account in a case," and approaches matters in a "persuasive, measured and calm" manner. (Chambers UK 2012)
    • "Marie Demetriou is ‘an iron fist in a velvet glove'" (Legal 500 2011)
    • "Marie Demetriou gives ‘clear and concise practical advice'" (Legal 500 2011)
    • "a great force to have on your side for all public and EU matters" (Chambers & Partners 2011)
    • "untiring" and "terribly bright and ever so good to work with" and has "notable experience of acting for central government, corporations and individuals in high-profile judicial review challenges" (Chambers & Partners 2011, Administrative & Public Law,)
    • "absolutely fantastic", "superb drafting", "very good insight" (Legal 500 2010, EU and competition)
    • "bright, quickly grasps complex issues and is generally a pleasure to work with" (Chambers & Partners 2010, Competition/European Law)
    • "Clients consider her one of the fastest-rising juniors at the Bar, viewing her as someone who ‘fights hard for clients, often against the toughest of odds'" (Chambers & Partners 2010, Telecommunications)
    • "impeccable intellect and extremely charming demeanour."; "professional manner and magnificent understanding of Competition and EU law,"; "she knows intimately how the European court functions, which is always a plus" (Chambers & Partners, 2009)
    • "displays excellence due to her superb knowledge of the European courts" (Chambers & Partners, 2009)
    • remarked upon for her flexibility and superlative grasp of competition and general European law issues (Chambers & Partners, 2008)