International Arbitration: No State Immunity Defence Against Registration of ICSID Awards in English Courts

In a judgment given on Wednesday 4 March 2026, the UK Supreme Court (the Supreme Court) ruled that:

• article 54¹ of the 1965 Convention on the Settlement of Investment Disputes between States and Nationals of Other States (the ICSID Convention) constitutes a clear submission to jurisdiction on the part of states for the purposes of recognising and enforcing ICSID awards; and
• by agreeing to be bound by article 54(1) of the ICSID Convention, states had waived sovereign immunity and submitted to the jurisdiction of the English courts by agreement within the meaning of section 2(2) of the State Immunity Act 1978 (the SIA 1978).² 

Accordingly, claimants in the arbitral proceedings were entitled to have the underlying ICSID arbitration awards registered as final judgements against those states by the High Court of England & Wales (the High Court).

A brief case note follows. The full judgment can be read here: The Kingdom of Spain v Infrastructure Services Luxembourg S.À.R.L. and another; Republic of Zimbabwe v Border Timbers Ltd and another [2026] UKSC 9.

The Facts

This appeal arose from two underlying sets of proceedings:

The Spain Proceedings

Infrastructure Services Luxembourg S.À.R.L. and Energia Termosolar BV (the Infrastructure Claimants) invested in renewable energy facilities in Spain in 2011, on the strength of Spanish law provisions providing that the owners of renewable energy facilities located in Spain would receive a reasonable return on their investment. Subsequent changes to the regulatory regime damaged those investments, and the Infrastructure Claimants started an arbitration against the Kingdom of Spain (Spain) under article 26 of the Energy Charter Treaty (the ECT) and the ICSID Convention, for breach of the fair and equitable treatment standard.

The Infrastructure Claimants were successful in that claim and awarded damages of circa €120 million in 2019. On 4 June 2021, the Infrastructure Claimants applied to the High Court to register the arbitration award as a judgment.

The Zimbabwe Proceedings

Border Timbers Ltd and Hangani Development Co. (Private) Ltd (the Border Claimants) invested in land in Zimbabwe, which was later expropriated without compensation. The Border Claimants started an arbitration against the Republic of Zimbabwe (Zimbabwe) pursuant to the Switzerland-Zimbabwe bilateral investment treaty, which provides for the resolution of investor-state disputes pursuant to the ICSID Convention.

The Border Claimants were successful in that claim and awarded damages of circa $125 million in 2015. On 15 September 2021, the Border Claimants applied to the High Court to register the arbitration award as a judgment.

The Appeal

In the High Court proceedings, and subsequently before the Court of Appeal, Spain and Zimbabwe sought, unsuccessfully, to resist registration of the arbitration awards, on the basis that section 1(1) of the SIA 1978 granted them immunity from the adjudicative jurisdiction of the English courts. Spain and Zimbabwe were granted permission to appeal to the Supreme Court on two grounds:

• By agreeing to be bound by article 54(1) of the ICSID Convention, did Spain and Zimbabwe submit to the jurisdiction of the English courts by agreement, within the meaning of section 2(2) SIA 1978, such that they do not enjoy immunity from adjudicative jurisdiction with respect to the proceedings for registration of an ICSID award?
  
  
• Did Spain and Zimbabwe agree to arbitrate with the Infrastructure Claimants and Border Claimants respectively, within the meaning of section 9(1) of the SIA 1978 (providing that where a state agreed to submit a dispute to arbitration, that state was not immune to proceedings in the courts of the UK in relation to the arbitration), such that they do not enjoy immunity from adjudicative jurisdiction with respect to the proceedings for registration of an ICSID award?

The Decision

The Supreme Court held that, by agreeing to be bound by article 54(1) of the ICSID Convention, Spain and Zimbabwe had submitted to the jurisdiction of the English courts by agreement within the meaning of section 2(2) SIA 1978 and did not enjoy immunity from adjudicative jurisdiction with respect to the registration of an ICSID award. Having found accordingly, the Supreme Court determined it unnecessary to hear argument on or deal with the second ground of appeal.

Central to the Supreme Court’s reasoning was the consideration that a waiver of immunity by treaty requires a clear and unequivocal expression of the state’s consent to the exercise of jurisdiction. The Supreme Court thus indicated that the appropriate test is whether the words used in the treaty necessarily lead to the conclusion that the state has submitted to jurisdiction, which it considered the ICSID Convention did:

• Article 53(1) contains an agreement by each contracting party that awards rendered under the ICSID Convention shall be final and binding, and that an enforcing court cannot re-examine the award on its merits or refuse enforcement (except as otherwise provided by the ICSID Convention or to the extent that enforcement has been stayed pursuant to the relevant provisions of the ICSID Convention);
  
  
• Under article 54(1) each contracting state is obliged to recognise as binding and enforce the pecuniary obligations of an award rendered pursuant to the ICSID Convention as if it were a final judgment of its own courts. Accordingly, a contracting state not only assumes that obligation to recognise and enforce ICSID awards but also consents to the fact that all other contracting states are undertaking this same obligation;
  
  
• The waiver of state immunity follows from the fact that each contracting state has agreed that all other contracting states are obliged to recognise and enforce ICSID awards, including as against them in the territories of those other contracting states, on a mutual and reciprocal basis; and
  
  
• This waiver necessarily involves an express acceptance by each contracting state that if an ICSID award is issued against it, then every other contracting state must exercise jurisdiction, if requested, to recognise and enforce that award.

Based on the above, the Supreme Court found that Article 54(1) was a clear and unequivocal submission to the adjudicative jurisdiction of the English courts for the purposes of recognising and enforcing the arbitral awards against Spain and Zimbabwe, and entirely consistent with the object and purpose of the ICSID Convention.

Interestingly, in its reasoning, the Supreme Court also referred to the importance of consistent interpretation of international instruments and the intention that international treaties be interpreted by the courts of all the state parties as having the same meaning. It specifically noted that there was broad international consensus as to the meaning and effect of article 54(1) of the ICSID Convention, having been interpreted as a waiver of adjudicative immunity by each contracting state (and, where domestically relevant, a submission to jurisdiction) by the courts of Australia, New Zealand, Malaysia, and the United States.

The Supreme Court did not interfere with a prior order of the Court of Appeal, remitting Zimbabwe’s application to set aside back to the High Court for directions to determine certain other non-immunity defences.

Our international disputes team is on hand to assist with any queries following this decision.

^{1 Obliging contracting States to recognise an award rendered pursuant to the ICSID Convention as binding and enforce the pecuniary obligations imposed by that award within its territories as if it were a final judgment of a court in that State}

^{2 A State is not immune as respects proceedings in respect of which it has submitted to the jurisdiction of the courts of the United Kingdom, whether that is after the dispute giving rise to the proceedings has arisen or by a prior written agreement}