Public International Law: A UK-wide Overview

Despite ongoing global political uncertainty and alleged threats to the rule of law, international law and international dispute resolution continue to play a central role in resolving complex disputes between states, as well as between private entities and states. Whether before international tribunals or domestic courts, international law remains a dynamic and flourishing field. This contribution considers four areas that have been particularly active:

• state immunity and domestic courts;
• investment treaty arbitration and domestic courts;
• the International Court of Justice; and
• the International Tribunal on the Law of the Sea.

State Immunity and Domestic Courts

State immunity is a cornerstone of international law. As a general matter (and subject to notable exceptions) it protects a state from being subject to the jurisdiction of another state’s courts (so-called “jurisdictional immunity”) and from enforcement measures against its property (“enforcement immunity”). Some of the most significant recent developments concerning state immunity have occurred before domestic courts.

For example, on 8 November 2024, the BVI Commercial Court delivered a judgment regarding a state’s consent to the execution of its property under Section 13(3) of the State Immunity Act (SIA), which applies to the BVI through the State Immunity (Overseas Territories) Order 1979. The underlying dispute arose from an investment-treaty award in Zhongshan Fucheng Industrial Investment Co Ltd v Federal Republic of Nigeria, in which an UNCITRAL tribunal found that Nigeria had breached the China-Nigeria bilateral investment treaty (“China-Nigeria BIT”) due to actions taken by Nigerian state actors and entities.

After Nigeria failed to comply with the award, Zhongshan initiated enforcement proceedings, including in the BVI, and sought to attach a debt owed to Nigeria by a BVI company: Process & Industrial Developments Ltd (“P&ID”). Nigeria argued that this property was immune from execution under Section 13(2)(b) of the SIA. Zhongshan, however, contended that Nigeria had consented to execution against its property through Article 9(6) of the China-Nigeria BIT, which states that the award is final and binding and that Nigeria “commits … to the enforcement of the award.” Thus, Zhongshan maintained that Nigeria’s consent to execution was explicit in the BIT.

Nigeria countered that Articles 54 and 55 of the ICSID Convention distinguish between recognition and enforcement, on the one hand, and execution, on the other. The BVI Commercial Court rejected this argument, noting that the ICSID Convention is a separate treaty addressing a different subject matter. Furthermore, if China or Nigeria had intended to limit the waiver of immunity to enforcement in the narrower sense proposed by Nigeria, they could have done so as in Articles 54 and 55 of the ICSID Convention. As a result, the court dismissed Nigeria’s immunity claims and confirmed the provisional attachment of the debt owed by P&ID to Nigeria.

Investment Treaty Arbitration and Domestic Courts

The intersection between investment treaty arbitration and domestic courts has become increasingly prominent in recent years, including in the context of the proliferation of investment treaty awards against states in the renewable energy sector.

In two combined cases – (1) Infrastructure Services Luxembourg S.à.r.l and Energia Termosolar B.V. v The Kingdom of Spain; and (2) Border Timbers Limited and Hangani Development Co. (Private) Limited v Republic of Zimbabwe – the UK Supreme Court is set to decide whether states can rely on state immunity to set aside the registration of ICSID arbitral awards in the United Kingdom to which they do not consent to enforcement. The underlying disputes were two separate ICSID arbitrations on different issues, and two High Court decisions were handed down in each case whereby the High Court dismissed the states’ objections to the recognition of the ICSID awards based on state immunity at the stage of registration of an ICSID award. The appeals were heard together, and the Court of Appeal dismissed the states’ objections confirming that state immunity does not apply to registration of ICSID awards. The forthcoming judgment of the UK Supreme Court will shed light on an important area of international law, particularly given the numerous ICSID awards that are enforced against sovereign states in England.

The International Court of Justice

The International Court of Justice (the “ICJ”) in The Hague maintains an active docket with 23 contentious cases and one advisory opinion – on the right to strike – pending before it. Interestingly, several cases involve issues of state immunity and consular/diplomatic immunity. While the ICJ is not specifically a human rights court, it is notable that several pending cases stem from alleged violations of the Convention on the Elimination of Racial Discrimination, the Convention against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment, and the Convention on the Prevention and Punishment of the Crime of Genocide.

Although it is sometimes said that international law is in a state of flux, and the UN Security Council is largely deadlocked, the progress of so many prominent pending cases seems to suggest that international law remains particularly relevant and states recognise the jurisdiction and authority of the ICJ as the principal judicial organ of the United Nations to resolve international disputes or give an advisory opinion on important legal questions.

The International Tribunal on the Law of the Sea

Another prolific area of disputes is the international law of the sea. The International Tribunal on the Law of the Sea (ITLOS) in Hamburg is currently involved in two cases before it, The M/T “Heroic Idun” (No. 2) Case (Marshall Islands/Equatorial Guinea) and The “Zheng He” Case (Luxembourg v Mexico). Both disputes involve states members to the United Nations Convention on the Law of the Sea (UNCLOS) and each case relates to actions taken against respective vessels with the flag of an UNCLOS member state. These contentious cases sit alongside the Advisory Opinion on Climate Change and International Law that the ITLOS unanimously issued in 2024. This was the first advisory opinion that an international tribunal issues on the matter (the other opinions of the International Court of Justice and the Inter-American Court of Human Rights followed in 2025). These cases are a demonstration of the relevance of the law of the sea in international law and more broadly in the context of natural (including marine) resources and activities.