On 4 March 2026, the Supreme Court of the United Kingdom (the “Supreme Court”) held in Kingdom of Spain v Infrastructure Services Luxembourg S.À.R.L. and Republic of Zimbabwe v Border Timbers Ltd that Spain and Zimbabwe (the “States”) could not invoke state immunity to resist the registration in England of ICSID awards rendered against them. The Court concluded that, by agreeing to Article 54(1) of the 1965 Convention on the Settlement of Investment Disputes between States and Nationals of Other States (the “ICSID Convention”), contracting states clearly submit to the adjudicative jurisdiction of other contracting states’ courts for recognition and enforcement proceedings. What remains protected is immunity from execution against state assets under Article 55. In doing so, the Supreme Court placed English law firmly within an emerging international consensus on the treatment of ICSID awards.
Background
The first arbitration, Kingdom of Spain v Infrastructure Services Luxembourg S.À.R.L. and another, had resulted in an EUR 101 million award against Spain on the basis of claims by companies domiciled in Luxembourg and the Netherlands that changes made by Spain to its regulatory regime governing its energy market breached the Energy Charter Treaty (the “ECT”) in respect of their investment in renewable energy facilities in Spain.[1] The second arbitration, Republic of Zimbabwe v Border Timbers Ltd and another, had ended with a USD 125 million award against Zimbabwe as a result of claims by Swiss companies that Zimbabwe had expropriated their land investments without compensation.[2]
In both cases, the successful investors applied to register the awards in the High Court under the Arbitration Act as if they were final judgments from the High Court, which the States opposed by invoking their sovereign immunity under Section 1(1) of the State Immunity Act 1978 (the “SIA”).[3] The lower courts rejected those objections, and the States appealed to the Supreme Court.[4]
The Supreme Court
On appeal, the primary issue was whether Spain and Zimbabwe waived state immunity and submitted to the jurisdiction of the English courts by agreement within the meaning of Section 2(2) of the SIA by becoming parties to the ICSID Convention. This required the court to answer two questions: (1) What is the test for deciding whether there has been a prior written agreement to submit to the jurisdiction under Section 2(2) of the SIA?[5] and (2) Does Article 54(1) meet the test under Section 2(2) of the SIA?[6]
Concerning the first question, the States, on the one hand, argued that state immunity is a matter of such importance that an agreement to waive it must be express, using words such as “waiver” or “submission”.[7] The investors, on the other hand, argued that an express waiver need not use the terms “waiver”, “submission” or “immunity”, but could instead include a necessary implication from the express words used when the interpretative process required by Articles 31 and 32 of the Vienna Convention on the Law of Treaties 1969 (the “Vienna Convention”) is applied to them.[8]
After examining English courts’ prior judgments in cases such as R v Bow Street Magistrate, Ex parte Pinochet (No 3) [2000] 1 AC 147,[9] NML Capital Ltd v Republic of Argentina [2011] 2 AC 495,[10] General Dynamics United Kingdom Ltd v State of Libya [2025] EWCA Civ 134, [2025] 4 WLR 34,[11] as well as Argentine Republic v. Amerada Hess Shipping Corporation, 488 US 428 (1989) by the United States Supreme Court,[12] the Supreme Court ultimately agreed with the investors, holding that “the test is whether the words used necessarily lead to the conclusion that the state has submitted to the jurisdiction.”[13]
Moving on to the second question, the application of the test, the Supreme Court noted that the answer to this question depends on an exercise of treaty interpretation based on Articles 31 and 32 of the Vienna Convention.[14]
The Supreme Court recalled that the “clear focus” of Article 31 of the Vienna Convention, which states that a “treaty shall be interpreted in good faith in accordance with the ordinary meaning to be given to the terms of the treaty in their context and in the light of its object and purpose”, is “on seeking to ascertain the ordinary meaning of the relevant terms of the treaty having regard to context, object and purpose of the treaty as ‘a single combined operation’”.[15]
The court then noted that Article 32 of the Vienna Convention, which provides that “[r]ecourse may be had to supplementary means of interpretation, including the preparatory work of the treaty and the circumstances of its conclusion, in order to confirm the meaning resulting from the application of article 31”, allows for the consideration of supplementary material to confirm the ordinary meaning of a treaty, but emphasised that “the supplementary means of interpretation in article 32 cannot be used to change or contradict the meaning resulting from the application of article 31.”[16]
Finally, the Supreme Court recalled that it is well-established that the text of an international treaty is intended to be given the same uniform meaning by all state parties to it, meaning that regard should be had to any consensus that exists among national courts as to the question of interpretation.[17]
The court considered each of these factors in turn.
Ordinary meaning
The Supreme Court first turned to the ordinary meaning of Articles 53-55 of the ICSID Convention.[18] According to the court, Articles 53 to 55 of the ICSID Convention create a system in which ICSID awards are final, binding, and must be recognised and enforced by every contracting state as though they were final domestic court judgments. The court reasoned that this structure leaves no room for a state to invoke adjudicative immunity at the recognition and enforcement stage.
The court pointed out that Article 53 makes awards final and binding, with no merits review by enforcing courts, except where enforcement has been stayed,[19] while Article 54(1) then requires each contracting state to recognise and enforce the pecuniary obligations in an ICSID award as if it were a final judgment of its own courts.[20] Because this obligation is mutual and reciprocal, each state has accepted not only that it must enforce awards, but also that awards against it may be enforced in the courts of other contracting states.[21]
The Supreme Court then noted that the ICSID Convention distinguishes sharply between “recognition and enforcement” and “execution”.[22] Recognition and enforcement come first under Article 54(1) and (2).[23] Execution, governed by Article 54(3), depends on the law of the state where enforcement is sought.[24] Article 55 expressly preserves only immunity from execution.[25] The court highlighted this sharp distinction, recognising that the Convention saves immunity from seizure of assets, but not immunity from the earlier judicial step of recognising and enforcing the award.[26]
On that basis, the court concluded that contracting states have, by agreeing to Article 54(1), waived reliance on adjudicative immunity in recognition and enforcement proceedings.[27] A state cannot both agree that other contracting states “shall” enforce ICSID awards against it and, at the same time, claim immunity that would prevent those states from doing so.[28]
Context
The Supreme Court then considered the context of the relevant provisions. Looking at the wider treaty framework, it said Article 54(1) cannot be read narrowly as a mere procedural promise. Instead, it sits within a closed enforcement system in which national courts must recognise and enforce ICSID awards without reopening the merits or relying on the usual public policy objections.[29]
The court stressed that states cannot avoid enforcement by raising challenges that the Convention already assigns to the ICSID process itself, such as annulment or jurisdictional objections.[30] Although immunity from execution may still protect state assets later at the stage of collection, that does not alter the earlier duty to recognise and enforce the award.[31] In the court’s view, the ICSID Convention creates a network of reciprocal obligations owed by every contracting state to every other, and the whole system depends on each state honouring those commitments.[32]
Articles 27 and 69 of the ICSID Convention reinforce that structure by showing that compliance with awards is a matter of collective treaty concern and that states must take whatever steps are necessary to make the ICSID Convention effective domestically.[33] Against that background, the court rejected the argument that disputes could simply be left to inter-state remedies under Article 64, holding that the treaty context instead supports the conclusion that contracting states have accepted adjudicative jurisdiction for recognition and enforcement of ICSID awards.[34]
Object and Purpose
On examining the object and purpose of the ICSID Convention, the Supreme Court recognised that it was designed to encourage foreign investment by reducing sovereign risk, especially the risk that a host state might interfere with an investment and then avoid meaningful accountability.[35] To achieve that, the court again noted that the Convention created a closed and reciprocal enforcement system: once an ICSID award is authenticated, national courts must recognise and enforce it without reopening the merits.[36]
The court drew support from the Convention’s preamble, its emphasis on compliance with awards, and the broader structure of mutual obligations between contracting states.[37] It also relied on R v Bow Street Magistrate, Ex parte Pinochet (No 3) by analogy, explaining that where a treaty creates a legal regime that would be undermined by allowing immunity, the better reading is that immunity cannot stand in the way.[38]
Although the court accepted that R v Bow Street Magistrate, Ex parte Pinochet (No 3) was a more extreme case involving immunity in cases of official torture, it held that the same logic applied here because allowing adjudicative immunity would seriously weaken one of ICSID’s central protections, namely the ability to treat an award like a final domestic judgment.[39]
Indeed, the Supreme Court said the present case was particularly strong because Article 54(1) imposes not merely a discretion to act, but an obligation to achieve a result: recognition and enforcement of the award.[40]
It therefore concluded that Article 54(1) of the ICSID Convention amounts to a clear and unequivocal submission by contracting states to the adjudicative jurisdiction of national courts for recognition and enforcement, while preserving immunity only at the later stage of execution.[41]
Travaux Préparatoires
Though the Supreme Court concluded that the meaning derived from the Article 31 analysis was clear and did not, therefore, necessitate recourse to supplementary means of interpretation under Article 32 of the Vienna Convention, it nonetheless analysed the travaux préparatoires, or preparatory work, of the ICSID Convention, if only to confirm the meaning arrived at through its Article 31 exercise.[42]
In particular, the preparatory materials showed that the drafters consistently intended ICSID awards, including awards against states, to be treated like final domestic judgments and to be enforceable on that basis.[43] The real concern during drafting was not immunity from being brought before a court for recognition and enforcement, but immunity from execution against state assets, which is why Article 55 was added expressly to preserve immunity at that later stage.[44]
The court emphasised that nothing in the drafting history suggested that adjudicative immunity was meant to block registration or recognition of an award in domestic courts.[45] Although some materials showed that one important purpose of Article 54 was to help states enforce awards against investors, the court said the same provision was always intended to work both ways and to give investors equivalent rights against states.[46]
In the Supreme Court’s view, the travaux therefore reinforced the conclusion that contracting states accepted recognition and enforcement proceedings in other contracting states, while preserving immunity only from execution.[47]
Principle of Consistent Interpretation
Finally, the Supreme Court emphasised that, as set out in Islam v Secretary of State for the Home Department, treaties like the ICSID Convention should, so far as possible, be interpreted uniformly across all contracting states, particularly in situations, such as here, where there is already broad international agreement on the meaning of the treaty.[48] It noted that courts in Australia, New Zealand, Malaysia, and the United States have all treated Article 54(1) as amounting to a waiver of adjudicative immunity, or at least a submission to the jurisdiction of domestic courts for recognition and enforcement proceedings.[49]
The court then reviewed those authorities and found them consistent with its own analysis: contracting states have accepted that ICSID awards may be recognised and enforced in other contracting states, while immunity remains relevant only at the later stage of execution against assets.[50] Although the states relied on a contrary decision from the British Virgin Islands, the Supreme Court gave it little weight, saying it failed to account for the reciprocal structure of Articles 53 and 54 and the fact that, by joining the ICSID Convention, each state accepted not only its own obligations but also the corresponding obligations of all other contracting states.[51]
Practical Effect
The practical effect of the judgment is substantial, but it should not be overstated.
The decision makes it harder for states to resist the registration of ICSID awards in England by invoking adjudicative immunity. That is an important gain for award creditors and, indeed, for the broader credibility of the ICSID system. It removes a threshold obstacle that, if accepted, would have hollowed out the promise of Article 54.[52]
At the same time, the Supreme Court’s decision does not foreclose all possible challenges by states to award registration. For example, states may still have recourse to non-immunity defences, such as those based on arguments of the nullity of the underlying award.[53]
Likewise, the judgment leaves untouched the more difficult question: whether the creditor will be able to enforce against state assets in practice. As the Supreme Court noted numerous times, immunity from execution remains preserved, and in many cases, that is where the real battle lies. As Emma Johnson and Elinor Thomas of Ashurst point out, “the sharp distinction highlighted by the Court between registration and enforcement of ICSID awards, on the one hand, and execution against state assets, on the other, means that considerable uncertainty remains as to the extent to which investors will, in fact, be able to monetise ICSID awards.”[54]
In any event, commentators, like the Supreme Court itself, have been quick to highlight that “the ruling ‘adds further weight to the international consensus that ICSID awards must be complied with and enforced’.”[55] This consensus will be discussed further in the next section.
Comparative Significance
What makes the judgment particularly interesting is not only that the Supreme Court expressly placed its analysis in a comparative context, but also that it appears to have undertaken the most sustained analysis to date of Article 54(1) of the ICSID Convention through the interpretative framework of Articles 31 and 32 of the Vienna Convention. As noted above, the Court emphasised that treaties such as the ICSID Convention should, so far as possible, be interpreted uniformly across contracting states, especially where a broad body of international case law already points in a common direction.
Courts in several jurisdictions have adopted materially similar positions, although they have sometimes reached them through different domestic legal routes and often in a more compressed way.
In Australia, the High Court in Kingdom of Spain v Infrastructure Services Luxembourg S.À.R.L. also treated Articles 53 to 55 as creating a regime in which immunity from recognition and enforcement is displaced, while immunity from execution remains preserved.[56] The Australian judgment, like the UK Supreme Court’s, emphasised the need to keep those concepts separate.
In New Zealand, the High Court in Sodexo Pass International SAS v Hungary likewise interpreted the ICSID Convention in accordance with Article 31 of the Vienna Convention and treated Article 54 as imposing a mandatory regime of recognition that could not sensibly coexist with a claim to adjudicative immunity at that stage.[57]
In the Malaysian case, Republic of Zimbabwe v Elisabeth Regina Maria Gabriele Von Pezold & Ors, in which the Malaysian High Court referred to New Zealand’s Sodexo case, the Zimbabwe-related proceedings brought by members of the von Pezold group also proceeded on the basis that sovereign immunity did not bar recognition of the award but remained relevant at the execution stage.[58] That position closely mirrors the UK Court’s understanding of the Convention’s structure.
In the United States, the analysis has taken a somewhat different form because of the structure of the Foreign Sovereign Immunities Act. In Blue Ridge Investments, LLC v Republic of Argentina, the court relied on the statute’s implied waiver and arbitration exceptions.[59] Even so, the practical conclusion was similar: by joining the ICSID Convention and agreeing to its enforcement mechanisms, the state had contemplated enforcement proceedings in the courts of other contracting states.
France, which, unlike the other decisions mentioned here, was not expressly mentioned by the UK Supreme Court, occupies a somewhat different position in this comparative story. The classic decision in Société Ouest Africaine des Bétons Industriels c. Senegal predates the recent wave of ICSID immunity litigation, but it anticipated an important part of the modern analysis.[60] The French courts distinguished between exequatur of an ICSID award and measures of execution against state assets, treating only the latter as engaging immunity from execution. In that sense, the French case law can be seen less as part of the current trend than as an early precursor to it.
Seen in this light, the UK Supreme Court did not create a new doctrine. Rather, it supplied what is arguably one of the most fully reasoned accounts to date of why Article 54(1) entails a contracting state’s submission to adjudicative jurisdiction for recognition and enforcement proceedings, while leaving immunity from execution intact. The judgment, therefore, matters not simply because it aligns the United Kingdom with an emerging international consensus, but because it may become the leading common law exposition of the doctrinal basis for that consensus.
Conclusion
The UK Supreme Court’s decision is important not because it abolishes state immunity in the ICSID context, but because it clarifies where immunity ends and where it remains in an important international jurisdiction. In England, contracting states cannot invoke adjudicative immunity to prevent the recognition and enforcement of ICSID awards under Article 54. What they retain is immunity from execution, preserved by Article 55 and domestic law.
That distinction is central to the architecture of the ICSID Convention, and the Supreme Court’s judgment gives it perhaps its clearest judicial expression to date. It also places the United Kingdom firmly alongside Australia, New Zealand, Malaysia, the United States, and the earlier French authorities in recognising that Article 54 would be deprived of much of its force if states could use immunity to block registration at the threshold.
For investors, the decision increases certainty at the recognition stage. For states, it confirms that joining the ICSID Convention carries real jurisdictional consequences before the courts of other contracting states. And for the wider law of investment arbitration, it marks another step towards a more settled and internationally coherent understanding of how ICSID awards are to be treated in domestic courts.
If you require assistance bringing an arbitration claim against a sovereign state, please contact Aceris Law for more information.
[1] The Kingdom of Spain (Appellant) v Infrastructure Services Luxembourg S.À.R.L. and another (Respondents); Republic of Zimbabwe (Appellant) v Border Timbers Ltd and another (Respondents) [2026] UKSC 9, paras. 3-5.
[2] Id., para. 10.
[3] Id., paras. 7-8, 12.
[4] Id., para. 16.
[5] Id., s. V.
[6] Id., s. VI.
[7] Id., para. 43.
[8] Id., para. 43.
[9] Id., para. 49.
[10] Id., para. 58.
[11] Id., para. 67.
[12] Id., para. 66.
[13] Id., para. 69 (emphasis added).
[14] Id., para. 74.
[15] Id., para. 75.
[16] Id., para. 76.
[17] Id., para. 79.
[18] Id., para. 80.
[19] Id., para. 81.
[20] Id., para. 82.
[21] Id., para. 82.
[22] Id., para. 87.
[23] Id., para. 83.
[24] Id., para. 85.
[25] Id., para. 86.
[26] Id., paras. 87-88.
[27] Id., para. 89.
[28] Id., para. 92.
[29] Id., para. 98.
[30] Id., para. 99.
[31] Id., para. 100.
[32] Id., para. 102.
[33] Id., paras. 103-104.
[34] Id., para. 105.
[35] Id., para. 106.
[36] Id., paras. 107-108.
[37] Id., para. 107.
[38] Id., paras. 109-114.
[39] Id., para. 116.
[40] Id., para. 117.
[41] Id., para. 118.
[42] Id., para. 119.
[43] Id., para. 120.
[44] Id., para. 120.
[45] Id., para. 126.
[46] Id., paras. 129-133.
[47] Id., para. 120.
[48] Id., para. 134.
[49] Id., para. 135.
[50] Id., paras. 136-140.
[51] Id., paras. 141-142.
[52] E. Johnson and E. Thomas, UK Supreme Court Confirms States cannot use Sovereign Immunity to Resist Registration of ICSID Arbitration Awards, 10 March 2026, https://www.ashurst.com/en/insights/uk-supreme-court-confirms-states-cannot-use-sovereign-immunity/ (last accessed 18 March 2026).
[53] U.K. Supreme Court Confirms Sovereign States Do Not Enjoy Adjudicative Immunity in Relation to Recognition of ICSID Awards, 9 March 2026, https://www.duanemorris.com/alerts/uk_supreme_court_confirms_sovereign_states_do_not_enjoy_adjudicative_immunity_relation_0326.html (last accessed 18 March 2026).
[54] E. Johnson and E. Thomas, UK Supreme Court Confirms States cannot use Sovereign Immunity to Resist Registration of ICSID Arbitration Awards, 10 March 2026, https://www.ashurst.com/en/insights/uk-supreme-court-confirms-states-cannot-use-sovereign-immunity/ (last accessed 18 March 2026).
[55] UK court rules Spain cannot claim state immunity in renewable energy incentives dispute, 4 March 2026, https://www.reuters.com/sustainability/boards-policy-regulation/spain-cannot-claim-state-immunity-uk-renewable-energy-incentives-dispute-2026-03-04/ (last accessed 18 March 2026).
[56] Kingdom of Spain v Infrastructure Services Luxembourg S.À.R.L. [2021] FCAFC 3.
[57] Sodexo Pass International SAS v Hungary, CIV-2020-485-734 [2021] NZHC 371.
[58] Elisabeth Regina Maria Gabriele Von Pezold & Ors v Republic of Zimbabwe [2023] MLJU 2657.
[59] Blue Ridge Investments, L.L.C. v. Republic of Argentina, 735 F.3d 72 (2d Cir. 2013).
[60] Société Ouest Africaine des Bétons Industriels c. Sénégal, Civ. 1ère, 11 juin 1991, No. 90-11.282.