The Supreme Court of the United Kingdom has ruled that foreign states cannot rely on sovereign immunity to block the enforcement of arbitration awards issued under the ICSID Convention.
In Infrastructure Services Luxembourg S.à.r.l and another v Kingdom of Spain, decided on 4 March 2026, the Court unanimously dismissed Spain’s appeal and confirmed that ICSID awards can be registered and enforced in the United Kingdom without states invoking immunity to prevent the process.
The ruling clarifies how the State Immunity Act 1978 interacts with the UK’s obligations under the Arbitration (International Investment Disputes) Act 1966.
For investors and arbitration practitioners, the judgment reinforces London’s role as a jurisdiction where treaty arbitration awards can be recognised even when sovereign respondents resist enforcement.
The Dispute
The case arose from investment arbitration proceedings brought by Infrastructure Services Luxembourg S.à.r.l and Energia Termosolar B.V. against Spain.
The investors alleged that regulatory changes affecting Spain’s renewable-energy support regime breached the country’s obligations under international investment law.
An arbitral tribunal constituted under the ICSID framework ruled in favour of the investors and awarded approximately €101 million in compensation.
The investors then applied to register the award in England under the Arbitration (International Investment Disputes) Act 1966, which implements the UK’s obligations under the ICSID Convention.
Spain sought to have the registration set aside, arguing that as a sovereign state it was protected by immunity under the State Immunity Act 1978 and could not be subjected to enforcement proceedings in English courts.
The dispute had previously reached the Court of Appeal, which rejected Spain’s argument and held that participation in the ICSID Convention entails acceptance that awards may be recognised and enforced in other contracting states.
Spain appealed that decision to the UK Supreme Court.
The appeal was heard together with a related case involving Republic of Zimbabwe v Border Timbers Ltd, which raised similar issues concerning sovereign immunity and the enforcement of ICSID arbitration awards.
What the Court Decided
The Supreme Court dismissed Spain’s appeal.
The Court held that a state that has agreed to the ICSID Convention cannot rely on sovereign immunity to prevent the registration of an ICSID arbitration award in the courts of another contracting state.
The justices concluded that registering an ICSID award under the Arbitration (International Investment Disputes) Act 1966 does not involve a substantive determination of the dispute by the court.
Instead, the registration process is a procedural step required by the Convention to give effect to the award.
Because the court does not reconsider the merits of the underlying dispute, the process does not constitute the type of judicial determination from which sovereign immunity would normally protect a foreign state.
The ruling therefore upheld the earlier judgment of the Court of Appeal and confirmed that the investors were entitled to register the €101 million award in England.
How the Court Got There
The case required the Court to interpret the relationship between two legal frameworks: the ICSID Convention, which establishes a global system for investor–state arbitration, and the State Immunity Act 1978, which governs when foreign states can be subject to the jurisdiction of UK courts.
Article 54 of the ICSID Convention requires contracting states to recognise ICSID awards as binding and enforce them as if they were final judgments of their own courts.
Spain argued that this obligation did not amount to consent to domestic court proceedings and that sovereign immunity should therefore prevent enforcement in the UK.
The investors argued that participation in the ICSID system necessarily involves acceptance that domestic courts in other member states will play a limited role in recognising and enforcing awards.
The Supreme Court agreed with the investors’ position. It held that the ICSID Convention creates a self-contained enforcement regime in which national courts perform a narrowly defined administrative function when registering awards.
Because the courts do not re-examine the underlying dispute, the process does not engage the core concerns that sovereign immunity is intended to protect.
Why the Ruling Matters
For investors pursuing claims against states under bilateral investment treaties, arbitration awards are only meaningful if they can ultimately be enforced.
States sometimes resist payment even after losing arbitration, forcing investors to seek recognition of awards in national courts around the world.
The Supreme Court’s decision confirms that English courts will give effect to the ICSID enforcement framework established by treaty and implemented in domestic legislation.
The ruling therefore reinforces the UK’s position as an important jurisdiction for the enforcement of international arbitration awards.
Separate Opinions
The appeal was heard by a panel consisting of Lord Lloyd-Jones, Lord Briggs, Lord Sales, Lord Leggatt and Lady Simler.
The Court delivered a unanimous judgment dismissing Spain’s appeal.
What Happens Next
Following the Supreme Court’s ruling, the investors remain entitled to rely on the registered arbitration award in England.
The judgment resolves Spain’s attempt to invoke sovereign immunity to prevent the registration of the ICSID award under UK law.
More broadly, the decision confirms that ICSID arbitration awards can be registered and enforced in English courts and that states party to the ICSID Convention cannot rely on sovereign immunity to block that process.
Case details
Court: Supreme Court of the United Kingdom
Date: 4 March 2026
Case: Infrastructure Services Luxembourg S.à.r.l and another v Kingdom of Spain
Neutral citation: [2026] UKSC 9
Docket number: UKSC/2024/0155
Area of law: International arbitration / sovereign immunity
Result: Spain’s appeal dismissed
People Also Ask
What is the ICSID Convention?
The ICSID Convention is an international treaty that establishes a system for resolving disputes between foreign investors and states through arbitration. Awards issued under the Convention are enforceable in all contracting states.
What did the UK Supreme Court decide in Infrastructure Services v Spain?
The Court ruled that Spain could not rely on sovereign immunity to challenge the registration of an ICSID arbitration award in England. The appeal was dismissed and the award remained enforceable.
Why are ICSID arbitration awards important?
ICSID awards allow investors to recover damages when states breach investment treaty obligations. The Convention ensures those awards can be recognised and enforced across member states.
What is sovereign immunity under UK law?
Sovereign immunity is a principle under the State Immunity Act 1978 that generally protects foreign states from being sued in UK courts, subject to certain exceptions.
Why does this ruling matter for international arbitration?
The decision confirms that English courts will recognise and enforce ICSID awards against states that are parties to the Convention, strengthening London’s role in the global arbitration system.
