ICSID Article 54(1) as a Treaty-Based Submission Waiving Adjudicative State Immunity for UK Registration and Enforcement

Case:

The Kingdom of Spain v Infrastructure Services Luxembourg S.A.R.L. & Anor

Citation:

[2026] UKSC 9

Court:

United Kingdom Supreme Court

Date:

2026-03-04

1. Introduction

This Supreme Court decision determines whether foreign states may invoke state immunity from adjudicative jurisdiction to set aside the registration in England and Wales of adverse ICSID investment arbitration awards under the Arbitration (International Investment Disputes) Act 1966 (“the 1966 Act”).

Parties and awards

• Spain appeal: The Kingdom of Spain sought to set aside registration of an ICSID award in favour of Infrastructure Services Luxembourg S.À.R.L. and Energia Termosolar BV (together “Infrastructure”), arising out of renewable energy regulatory changes alleged to breach the Energy Charter Treaty 1994 (“the ECT”). Spain had challenged ICSID jurisdiction (including on “intra-EU” grounds) and pursued ICSID annulment without success.
• Zimbabwe appeal: The Republic of Zimbabwe sought to set aside registration of an ICSID award in favour of Border Timbers Ltd and Hangani Development Co. (Private) Ltd (together “Border Timbers”), arising from alleged uncompensated expropriation under a Zimbabwe–Switzerland bilateral investment treaty. Zimbabwe maintained it never agreed to arbitrate with these claimants (a jurisdictional objection rejected in ICSID proceedings).

Key issues framed by the Court

• Issue 1: Does agreeing to ICSID Convention article 54(1) amount to a submission to UK court jurisdiction under section 2(2) SIA 1978, displacing immunity for registration/enforcement proceedings?
• Issue 2: (Not decided) Did the states agree to arbitrate with the investors so as to engage the arbitration exception in section 9(1) SIA 1978?

The Supreme Court heard full argument on Issue 1 only, holding it dispositive and therefore declining to determine Issue 2.

2. Summary of the Judgment

The Supreme Court dismissed both appeals. It held that:

• Section 2(2) SIA 1978 is satisfied where treaty language, interpreted under public international law principles, contains a clear and unequivocal expression of consent to the exercise of jurisdiction; the word “waiver” (or similar) is not required.
• Properly interpreted under articles 31 and 32 of the Vienna Convention on the Law of Treaties 1969, ICSID Convention articles 53–55 create a reciprocal regime in which each contracting state agrees that every other contracting state shall recognise and enforce ICSID pecuniary obligations as a final domestic judgment.
• Article 55 preserves only immunity from execution; it does not preserve adjudicative immunity at the recognition/enforcement stage. Therefore, a contracting state cannot invoke adjudicative immunity to block registration/enforcement.

The Court left standing the Court of Appeal’s remittal in Zimbabwe’s case concerning reserved non-immunity defences (potentially within the narrow category mentioned in Micula v Romania [2020] UKSC 5, [2020] 1 WLR 1033).

3. Analysis

3.1 Precedents Cited

(a) The doctrinal baseline: state immunity as a rule with exceptions

The Court anchored state immunity in sovereign equality, quoting Jurisdictional Immunities of the State (Germany v Italy) (2012) ICJ Rep 99. Immunity is a procedural bar, but subject to exceptions and waiver, including by treaty arrangements imposing reciprocal jurisdictional obligations.

(b) What counts as “express” waiver/submission: rejecting an overly narrow approach

R v Bow Street Magistrate, Ex parte Pinochet (No 3) [2000] 1 AC 147 featured prominently, specifically Lord Goff’s dissent advocating that waiver by treaty must “always be express” and implying that absence of an explicit immunity/waiver clause is decisive. The Supreme Court treated that as too narrow, emphasising instead that what matters is whether consent is clear and unequivocal when the treaty is properly interpreted.

The Court’s approach is fortified by:

• NML Capital Ltd v Republic of Argentina [2011] 2 AC 495: a contractual clause allowing a foreign judgment to be enforced in other courts was held to be an unequivocal waiver/submission despite no “waiver” language. This decision functions as the domestic analogue for construing treaty wording as a submission where the ordinary meaning compels it.
• General Dynamics United Kingdom Ltd v State of Libya [2025] EWCA Civ 134, [2025] 4 WLR 34: although concerned with enforcement/execution consent under section 13(3) SIA 1978, Phillips LJ rejected importing extra “clear words” glosses beyond construing whether the words used express consent. The Supreme Court endorsed that reasoning and applied it to section 2(2).

In short, the judgment consolidates a domestic rule: “express” in section 2(2) is satisfied by clarity and necessary consequence, not by magic words.

(c) Treaty interpretation method and “necessary implication” from express terms

The Court relied on orthodox VCLT interpretation principles, citing:

• JTI Polska sp. z o.o. v Jakubowski [2024] AC 621 and Maritime Delimitation in the Indian Ocean (Somalia v Kenya) [2017] ICJ Rep 3 for the “single combined operation” of text, context, object and purpose under VCLT article 31.
• Fothergill v Monarch Airlines [1981] AC 251 and Effort Shipping Co Ltd v Linden Management S.A. and others [1998] AC 605 on limited recourse to travaux under VCLT article 32.

To illustrate how obligations can follow necessarily from express treaty terms (without “reading in”), the Court invoked:

• Application of the Convention on the Prevention and Punishment of the Crime of Genocide (Bosnia and Herzegovina v Serbia and Montenegro) Judgment [2007] ICJ Rep 43, where the ICJ derived a prohibition on committing genocide from an express obligation to prevent it—an example of deriving necessary consequences from express obligations.

(d) Distinguishing jurisdiction from immunity—but finding incompatibility here

States cited Case concerning the Arrest Warrant of 11 April 2000 (Democratic Republic of the Congo v Belgium) (2002) ICJ Rep 1 for the proposition that jurisdiction and immunity are distinct. The Supreme Court accepted the distinction but held it did not assist: article 54(1) obliges a judicial end-state (“as if” final judgment) that cannot be achieved if adjudicative immunity blocks the process.

(e) ICSID scheme as “closed” and the domestic court’s constrained role

Micula v Romania [2020] UKSC 5, [2020] 1 WLR 1033 influenced the Court’s description of ICSID as a self-contained enforcement system: once authenticity is shown, domestic courts cannot re-examine merits or refuse enforcement on public policy in the way they might under the New York Convention. That characterization supported the interpretation that article 54(1) is meant to be mandatory and effective, leaving only execution immunities intact via article 55 and any extremely narrow “final judgment” defences contemplated in Micula.

(f) Uniform international understanding

Consistent interpretation across contracting states was reinforced by reference to:

• Islam v Secretary of State for the Home Department [1999] 2 AC 629 (and also Basfar v Wong [2022] UKSC 20, [2023] AC 33) as domestic authority favouring uniformity where there is a consensus on treaty meaning.

The Court found broad alignment with foreign case law interpreting article 54(1) as a waiver of adjudicative immunity, including:

• Kingdom of Spain v Infrastructure Services Luxembourg S.à.r.l. [2023] HCA 11 (Australia)
• Sodexo Pass International SAS v Hungary [2021] NZHC 371 (New Zealand)
• Von Pezold v Zimbabwe WA-24NCC-322-07/2021 (27 November 2023) (Malaysia)
• Blue Ridge Investments LLC v Republic of Argentina (2012) 735 F.3d 72 (United States)

It treated Tethyan Copper Company Pty Limited v Islamic Republic of Pakistan BVIHC (Com) 2020/0196, 25 May 2021 as an outlier of limited persuasive weight due to its failure to engage with reciprocity and the structure of articles 53–55.

(g) Parliamentary materials: a clear rejection

The Court declined any reliance on Hansard, applying the strict conditions in Pepper (Inspector of Taxes) v Hart [1993] AC 593, and finding no ambiguity in section 2(2) requiring such resort.

3.2 Legal Reasoning

(a) The domestic law test under section 2(2) SIA 1978

The Court reframed the debate about “express” versus “implied” waiver into a single operative question: whether the treaty text, properly interpreted, contains a clear and unequivocal expression of the state’s consent to the exercise of jurisdiction. Importantly:

• No special formula is required (no need to say “we waive immunity”).
• Consent can be conveyed by what is “necessarily inherent” in the words and what “necessarily follows” from them.
• This is not “implying” a term into a treaty; it is interpreting the meaning and necessary legal effect of the terms chosen.

(b) Interpreting articles 53–55 ICSID: the decisive architecture

Applying VCLT article 31, the Court read the “recognition and enforcement” provisions as a coherent enforcement pathway:

• Article 53(1): awards are final, binding, and only subject to ICSID internal remedies (interpretation/revision/annulment). Domestic courts may not re-open merits.
• Article 54(1): “Each Contracting State shall” recognise and enforce pecuniary obligations “as if” final domestic judgment. This creates a reciprocal network: by ratifying, each state accepts that other states’ courts must do this in relation to awards against it.
• Article 54(3) and Article 55: execution is governed by local law, and immunity is preserved only “from execution”.

From that structure, the Court’s key inference is straightforward: if domestic courts must treat the award as a final judgment, they must be able to exercise the adjudicative function necessary to reach that recognition/enforcement status. Preserving adjudicative immunity would prevent contracting states from performing the very obligation article 54(1) imposes.

(c) Context, object and purpose: sovereign risk and mutual enforcement

The Court emphasised that the ICSID Convention’s purpose is to promote investment by reducing sovereign risk through reliable dispute resolution and effective cross-border enforcement. The Convention’s “mutual trust and confidence” model (as described in Micula) depends on mandatory recognition/enforcement. Allowing states to block registration by asserting adjudicative immunity would substantially undermine that purpose, even if it would not render the Convention entirely nugatory.

(d) Travaux préparatoires: confirmatory, not transformative

Although not needed, the Court reviewed travaux and found they confirm that debates about “immunity” during drafting were about immunity from execution, which was explicitly preserved by adding what became article 55. There was no indication that adjudicative immunity was meant to remain as a barrier to recognition/enforcement.

3.3 Impact

(a) Practical impact in the UK: registration/enforcement becomes immunity-proof (at the adjudicative stage)

• Contracting states cannot set aside registration of ICSID awards under the 1966 Act by invoking section 1(1) SIA 1978 adjudicative immunity.
• The litigation battleground shifts to:
  • Execution (where immunity remains preserved, and section 13 SIA 1978 will be central), and
  • Any narrowly available “final judgment” type defences left open by Micula (if and when properly engaged).

(b) Clarification of “express” submission across the SIA 1978

The judgment is likely to be cited beyond ICSID in cases involving treaty-based or contractual jurisdictional submissions: it resists a formalistic insistence on “waiver” language and reinforces an interpretive, clarity-based approach for section 2(2).

(c) International alignment and reduced fragmentation

By aligning with the “broad international consensus” identified (Australia/New Zealand/Malaysia/US), the decision reduces the risk of divergent interpretations of article 54(1) among contracting states—an anxiety expressed in the immunity context in Pinochet (No 3) (albeit in dissent).

(d) What the Court did not decide (and why that matters)

• Section 9(1) SIA 1978 (arbitration exception) remains undecided by the Supreme Court here. The Court of Appeal’s suggestion that English courts may need to satisfy themselves of a written arbitration agreement (and are not bound by an ICSID tribunal’s jurisdictional ruling) is not endorsed or rejected.
• Spain’s “intra-EU” arguments (ECT/TFEU) were not addressed. The decision therefore isolates the immunity point from broader questions about EU law constraints and ICSID jurisdiction.

4. Complex Concepts Simplified

• Adjudicative immunity vs immunity from execution:
  • Adjudicative immunity is immunity from being sued or subjected to a court’s adjudicative processes (eg, recognition/registration proceedings).
  • Immunity from execution is immunity from measures that seize or realise state property to satisfy a judgment/award.
  • This case concerns only the former; article 55 preserves only the latter.
• Recognition/enforcement vs execution (in ICSID terms):
  • Under article 54(1), the award must be treated “as if” it were a final domestic judgment—this is the recognition/enforcement stage.
  • Only after that can a creditor attempt coercive steps against assets (execution), which remains subject to domestic execution rules and immunity (articles 54(3) and 55).
• “Express” waiver without the word “waiver”:
  • “Express” does not mean “uses the word waiver”. It means the treaty’s words, interpreted normally, clearly and unequivocally communicate consent to jurisdiction.
  • The Court treats “necessary consequence” from the words as part of what the words mean, not as an “implied term”.
• Self-contained ICSID system:
  • ICSID awards are insulated from national court merits review; challenges are internal to ICSID (articles 50–52).
  • Domestic courts’ role in recognition/enforcement is therefore tightly constrained once authenticity is shown.

5. Conclusion

The Supreme Court has laid down a clear rule for UK proceedings under the 1966 Act: ICSID Convention article 54(1) is itself a prior written treaty submission under section 2(2) SIA 1978, amounting to a clear and unequivocal waiver of adjudicative state immunity for the purpose of recognising and enforcing (registering) ICSID pecuniary awards “as if” final High Court judgments. The judgment simultaneously preserves the orthodox boundary that immunity from execution remains intact, expressly safeguarded by article 55. In doctrinal terms, the case is equally significant for confirming that “express” submission in the SIA 1978 is a matter of clarity of meaning, not of formulaic wording, and that treaty obligations may negate immunity where their ordinary meaning is incompatible with its continued operation.