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Public International Law

The Public International Law Group has more than 30 years’ experience advising sovereign States and their emanations, international organisations and commercial entities on disputes before the domestic courts and international courts and tribunals, as well as advising on non-contentious matters.

Our team supports clients on a broad range of public international law issues, including privileges and immunities, enforcement, obtaining evidence for use in overseas proceedings, expropriation, the law of the sea, treaty law, State responsibility, international institutional law and the application of EU and UK sanctions rules. 

We also regularly advise on Investor-State arbitrations, with CMS specialists from across our network of global offices pooling their skills and expertise within the CMS Investment Arbitration Task Force.

Our experience includes advising:

  • Pakistan in successfully dismissing the Nuclear Disarmament Case brought by the Republic of the Marshall Islands before the International Court of Justice.
  • The Caribbean Regional Fisheries Mechanism (17 Member States) in Case 21 before the International Tribunal for the Law of the Sea in Hamburg.
  • The Government of a Caribbean country in a fisheries-related dispute with the European Commission.
  • Erste Group Bank AG in a treaty-based investment arbitration against the Republic of Croatia before the World Bank’s International Centre for Settlement of Investment Disputes (ARB/17/49).
  • The United States of America in relation to whether it is bound to consult with its local civilian employees about redundancies before closing a military base, and how domestic statutes should be interpreted to give effect to customary international law, United States of America v Nolan [2015] UKSC 63, Supreme Court.
  • The US Securities and Exchange Commission in its successful application for the continuance of a freezing injunction unanimously upheld by the Court of Appeal, in what is believed to be the first decision of its kind in granting the order to a foreign claimant without the requirement for a cross undertaking in damages, 
  • The US Secretary of State for Health in obtaining one of the first orders of its kind for disclosure by a third party under CPR5.4C(2) for the provision of various medical reports from the UK MMR litigation for use in the US MMR autism group litigation, Sayers & Ors v Smithkline Beecham Plc & Ors  [2007] EWHC 1346 (QB).
  • The United States of America in its successful assertion of state immunity in the House of Lords, Holland v Lampen-Wolfe [2000] 1 WLR1573.
  • Kuwait Airways and the State of Kuwait in connection with claims and associated appeals arising out of the invasion of Kuwait in 1990.  The resulting judgments re-wrote the law books on State Immunity and Act of State doctrine in the House of Lords, (1995) 1 WLR 1147 (HL); (2001) 1 WLR 429 (HL), (2002) (No. 6) 2 AC 883 (HL); and (2010) 2 S.C.R. 571.
  • Fugro, the world’s leading Geo-data specialist headquartered in The Netherlands, in connection with public international law, in particular the Law of the Sea, aspects of Fugro’s geo-data services (especially surveys) to its customers worldwide.
  • The Government of St Vincent and the Grenadines on its ongoing dispute with the European Commission following the black-listing of SVG due to alleged IUU fishing activities by SVG-flagged vessels.
  • Patel Engineering Limited (“PEL”), the largest private infrastructure and construction services company in India, in Patel Engineering Limited (India) v. The Republic of Mozambique (PCA Case No. 2020-21).
Awards & Recognitions
01
  • Quote
    "The solicitors I met were enthusiastic about their work and totally committed to the firm. They were diverse and interested in and supportive of students."
    Legal 500, 2026
  • Quote
    "I worked on a presentation to students with Roman Hryshyn-Hryshchuk, Karen Denny and Zainab Hodgson. They are all experts on international dispute resolution and state immunity in particular. They are knowledgeable, very capable and most impressive."
    Legal 500, 2026
  • Quote
    "Excellent team. Very experienced. They operate across different departments so as to provide best advice drawing from expertise in other areas of the firm."
    Legal 500, 2026
  • Quote
    "Karen Denny is exceptional. Very astute and a pleasure to work with."
    Legal 500, 2026
  • Quote
    "Karen Denny is not afraid to get into the detail of a case."
    Legal 500, 2024
  • Quote
    "Karen Denny is 'a star individual."
    Legal 500, 2024
  • Quote
    "The CMS team is strong across the board."
    Legal 500, 2024
  • Quote
    Diligent partners with close oversight of all matters. Excellent blue-sky thinking.’
    Legal 500, 2024
  • Quote
    "The CMS team are very good. They respond quickly and help to pull together advice in a coherent and user-friendly way."
    Chambers & Partners, 2024

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Events

  • United Kingdom
    20 Apr 2026

    Skills for Future Facing Teams: The Emotionally Intelligent Leader

  • United Kingdom
    21 Apr 2026

    On the Pulse webinar series 2026 - Spring/Summer

  • United Kingdom
    21 Apr 2026

    Future of Renewables Spring Seminars

  • United Kingdom
    22 Apr 2026

    Sustainable Buildings: Taking the Temperature in 2026

  • United Kingdom
    23 Apr 2026

    ESG: Breaking Down the Buzzword

  • United Kingdom
    28 Apr 2026

    Strategic expansion to India: A new chapter for UK higher education

  • United Kingdom
    28 Apr 2026

    IP Insights webinar series 2026

  • United Kingdom
    29 Apr 2026

    CMS Update Morning: Media, Sports and Entertainment

  • United Kingdom
    02 May 2026

    CMS at INTA 2026

  • United Kingdom
    05 May 2026

    Joint seminar with CMS and Tannenbaum Helpern - A global perspective on securing, maintaining, and enforcing...

  • United Kingdom
    05 May 2026

    Cross-Border Financial Services 2026 webinar series

  • United Kingdom
    07 May 2026

    A new era? The Employment Rights Act 2025 and AI in employment disputes

  • United Kingdom
    11 May 2026

    Skills for Future Facing Teams: The Adaptable Leader in Conflict

  • United Kingdom
    13 May 2026

    2026 ITechLaw World Technology Law Conference in Chicago

  • United Kingdom
    20 May 2026

    A new era? The Employment Rights Act 2025 and AI in employment disputes

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