Introduction
In a landmark decision for international arbitration and public international law, the Supreme Court has in The Kingdom of Spain v Infrastructure Services Luxembourg S.à.r.l.; Republic of Zimbabwe v Border Timbers Ltd [2026] UKSC 9 confirmed that states which are party to the ICSID Convention waive their immunity from the adjudicative jurisdiction of the English courts in proceedings to recognise and enforce ICSID arbitral awards. The judgment provides authoritative clarification on the interaction between the ICSID Convention and the State Immunity Act 1978, reinforcing the United Kingdom’s (UK) position as a proenforcement jurisdiction for investment arbitration awards.
Facts
The appeals arose from attempts by the Kingdom of Spain and the Republic of Zimbabwe to set aside the registration in England of ICSID arbitral awards made against them. In both cases, the successful investors sought registration of the awards under the Arbitration (International Investment Disputes) Act 1966, which gives effect to the UK’s obligations under the ICSID Convention. Spain and Zimbabwe resisted registration on the basis that they were immune from the jurisdiction of the English courts pursuant to section 1 of the State Immunity Act 1978. The High Court and Court of Appeal rejected those arguments, holding that the states had submitted to the jurisdiction of the English courts. Both states appealed to the Supreme Court.
Issues
The principal issue before the Supreme Court was whether, by ratifying the ICSID Convention, contracting states submit to the adjudicative jurisdiction of the courts of other contracting states, for the purposes of section 2(2) of the State Immunity Act 1978. In addressing that issue, the Court examined Articles 53 to 55 of the ICSID Convention. In particular, it considered whether the obligations of finality and binding effect under Article 53, together with the reciprocal obligation on contracting states under Article 54(1) to recognise and enforce ICSID awards as if they were final domestic judgments, constitute a clear and unequivocal waiver of adjudicative immunity, as distinct from immunity from execution against state assets.
The claimants had also argued that the State’s execution of investment treaties containing arbitration clauses constituted a separate basis for jurisdiction. However, the Supreme Court found it unnecessary to determine that issue in light of its conclusion under section 2(2).
Outcome
The Supreme Court unanimously dismissed both appeals. It held that, when read together, Articles 53 to 55 of the ICSID Convention establish a self‑contained enforcement regime that is fundamentally incompatible with the maintenance of adjudicative immunity. In particular, the Court emphasised that Article 53 renders ICSID awards final and binding on the parties, while Article 54(1) obliges each contracting state to recognise and enforce such awards as if they were final judgments of its own courts. By acceding to the ICSID Convention, each contracting state agrees not only to enforce awards domestically, but also to allow other contracting states to do the same. That reciprocal commitment amounts to a submission to jurisdiction within the meaning of section 2(2) of the State Immunity Act 1978.
The Court drew a clear distinction between adjudicative immunity and immunity from execution. While Article 55 of the ICSID Convention preserves immunity from execution against state property (absent exceptions to such immunity under applicable law), it does not preserve immunity from the prior step of recognition and enforcement. The absence of any such preservation, viewed against the binding and final character of ICSID awards under Article 53, confirmed that contracting states waive adjudicative immunity in enforcement proceedings. The Court emphasised that a waiver of immunity need not use express words such as “waiver” or “submission”, provided the treaty language clearly and unequivocally leads to that conclusion.
Comments
This decision provides important certainty for investors seeking to enforce ICSID awards in the UK. It confirms that states cannot rely on adjudicative immunity to resist recognition and enforcement of such awards, while preserving their ability to rely on immunity from execution at a later stage. The judgment aligns English law with the consensus of courts outside the European Union and underscores the central purpose of the ICSID Convention: to mitigate sovereign risk by ensuring reliable and effective enforcement of investment arbitration awards. It also reinforces the UK’s reputation as a jurisdiction committed to upholding international arbitration obligations and the rule of law.
