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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.

"Deep knowledge of international law and hardworking."

Legal 500, 2023

"The CMS team is very knowledgeable and delivers exceptional professional services."

Legal 500, 2023

"An eye for fine detail, thoroughness and top-notch team work."

Legal 500, 2023

“A very able team with particularly strong expertise in acting for states.”

Legal 500, UK 2022

“This practice stands out for its balanced combination of a solid theoretical grasp of public international law and its practical application.”

Legal 500, UK 2022

"The team at CMS is engaging and approachable. They have diverse interests and experiences, which they combine well on a case, as needed."

Legal 500, 2021

"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

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26/08/2022
High Court rules there is no im­munity to per­son­al in­jury claim arising...
Sum­mary The High Court has con­sidered the ap­plic­a­tion of the ex­cep­tion to state im­munity, con­tained in sec­tion 5 of the State Im­munity Act 1978 (“SIA”), in a per­son­al in­jury claim  com­menced by...
13/07/2022
No dip­lo­mat­ic im­munity for per­pet­rat­ors of mod­ern slavery
In a ground­break­ing judg­ment, the UK Su­preme Court has ruled, for the first time, that the al­leged ex­ploit­a­tion of a do­mest­ic work­er falls with­in the com­mer­cial activ­ity ex­cep­tion to a dip­lo­mat’s im­munity...
14/06/2022
High Court con­siders the ap­plic­a­tion of the ser­vice pro­ced­ures in sec­tion...
Sum­mary In a judg­ment handed down on 14 March 2022, the High Court has de­cided that the de­fend­ant na­tion­al flag car­ri­er of Sur­i­n­ame (re­ferred to as “SLM”) was not en­titled to be served with a Claim...
23/09/2021
EU Court of Justice rules against In­tra-EU ar­bit­ra­tion un­der the En­ergy...
On 2 Septem­ber 2021, the Court of Justice of the European Uni­on (CJEU) ruled that in­tra-EU ar­bit­ra­tions based on the En­ergy Charter Treaty (ECT) vi­ol­ate EU law.  The de­cision is likely to im­pact the...
22/07/2021
CMS In­ter­na­tion­al Dis­putes Di­gest - 2021 Sum­mer Edi­tion
Wel­come to the 2021 sum­mer edi­tion of our In­ter­na­tion­al Dis­putes Di­gest, a bi-an­nu­al pub­lic­a­tion fea­tur­ing ana­lys­is and com­ment­ary on the key trends cur­rently shap­ing the glob­al dis­pute res­ol­u­tion mar­ket.As...
16/12/2020
In­ter­na­tion­al Dis­putes Di­gest - Winter Edi­tion 2020
Wel­come to the winter edi­tion of the CMS In­ter­na­tion­al Dis­putes Di­gest, the bi­an­nu­al pub­lic­a­tion of CMS’ Dis­pute Res­ol­u­tion prac­tice fea­tur­ing ana­lys­is and com­ment­ary on the ma­jor trends shap­ing the...
09/12/2020
Is the sun set­ting on the En­ergy Charter Treaty? An up­date on the mod­ern­isa­tion...
On 2 Decem­ber 2020, the European Com­mis­sion (the “Com­mis­sion”) in­dic­ated that if “core EU ob­ject­ives” are not met as part of the on­go­ing ne­go­ti­ations to mod­ern­ise the En­ergy Charter Treaty (the...