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Public International Law

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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.

"Karen Denny is a class act. She always puts the client first, and has a deep interest in and knowledge of the public international law field."

Legal 500, 2021

"Karen Denny is outstanding. She has a breadth of knowledge in this area which is impressive. She is also excellent with clients."

Legal 500, 2021

"The CMS team is strong across the board."

Legal 500, 2024

Diligent partners with close oversight of all matters. Excellent blue-sky thinking.’

Legal 500, 2024

"The CMS team are very good. They respond quickly and help to pull together advice in a coherent and user-friendly way."

Chambers, 2024


CMS International Construction Study 2024
In recent years, construction and engineering businesses have faced a whole storm of headwinds. CMS, in partnership with YouGov, asked in-house lawyers about the biggest challenges of managing disputes in this environment - and how those challenges can be met.   Sixty-second summaryThe evolving nature of construction risk will see changes to standard contracts and negotiation positions. It may also bring more disputes, particularly where those changes lag behind project realities. Fewer than half the businesses we surveyed reported that the in-house legal or contract management team is always consulted at the start of a project to identify areas of risk and to establish appropriate risk management strategies. Most in-house lawyers believe their businesses could improve the way in which risk is managed during projects - often in a number of important ways. Despite the potential benefits, only 17% of the in-house lawyers we surveyed are using AI in disputes or contract management. Some say they will never use it. Most in-house lawyers believe their businesses have a lot of scope to improve the way that project risks are managed. AI has the potential to be a game-changer in this area by optimising processes, planning, scheduling and other elements of case management and by revolutionising the way a business handles its portfolio of contracts. 
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