At a time when serious questions are being asked about whether the international rules-based order is simply a “useful fiction”, repetition, by the Supreme Court in Zimbabwe v Border Timbers, of a passage in an ICJ judgment, Jurisdictional Immunities of the State (Germany v Italy), may have prompted a wry smile from the reader. The relevant passage stresses the important place in international law occupied by the fundamental principle of State immunity, which the ICJ said must be viewed together with the principle that each State possesses sovereignty over its own territory and that there flows from that sovereignty the jurisdiction of the State over events and persons within that territory.

The principal questions

In Border Timbers, the Supreme Court was asked whether, by agreeing to be bound by Article 51(1) of the ICSID Convention, the appellant States (Zimbabwe and Spain) had submitted to the jurisdiction of the English courts by agreement within the meaning of s.2(2) State Immunity Act 1978 (“SIA”) such that they did not enjoy immunity from adjudicative jurisdiction with respect to the proceedings under s.1(1) SIA.

To determine the answer to this overarching question, the Supreme Court considered: (1) the test for deciding whether there has been an agreement to submit to the jurisdiction under s.2(2) SIA; and (2) the correct interpretation of Articles 53 to 55 of the ICSID Convention as a matter of customary international law.

Agreement to submit to the jurisdiction

The Supreme Court emphasised that a waiver of immunity by treaty requires a clear and unequivocal expression of the State’s consent to the exercise of jurisdiction.  Whether this existed depended upon the interpretation of the treaty (in line with Articles 31 and 32 of the Vienna Convention). An expression of consent did not, the Supreme Court emphasised, require explicit words such as “waiver” or “submission”. In this respect, meaning is not just found in the express words of the treaty, but by what is necessarily inherent in those words and by what necessarily follows as a consequence of those words. Accordingly, when considering the waiver of state immunity by treaty, the test is whether the words used necessarily lead to the conclusion that the state has submitted to the jurisdiction.

To illustrate the point, the Supreme Court highlighted Pinochet (No.3). The offence of torture established by the Convention against Torture is limited to offences of torture committed in an official capacity. If States could meet allegations under the Torture Convention with a plea of immunity, it would render the terms of the Torture Convention redundant; the immunity would be exactly coextensive with the offence. In these circumstances, the parties to the Torture Convention must have been taken to have decided that immunity ratione materiae should not be available.

Interpretation of ICSID

Article 54(1) of the ICSID Convention provides that each Contracting State “shall recognise an award rendered pursuant to [it] as binding and enforce the pecuniary obligations imposed by that award within its territories as if it were a final judgment of a court in that State.” Applying the approach in the Vienna Convention, the Supreme Court concluded that the ordinary meaning of Article 54(1) was as a clear and unequivocal waiver of adjudicative immunity by state parties. Preservation of the immunity against execution, by way of Article 55 of the ICSID Convention, reinforced, rather than undermined, this conclusion.

Conclusion

I wrote about the first instance judgment of Dias J in Border Timbers v Zimbabwe well over 2 years ago, and noted at the time what a tour de force that judgment was. One might have thought that the outcome of the States’ appeals to the Court of Appeal (where judgment was delivered in October 2024) and the Supreme Court (judgment in March 2026) were both somewhat of a foregone conclusion. However, when a point is worth more than US$124m (as it is for Zimbabwe), even if the prospects of success are low, the point is likely worth taking, as perhaps is any action which delays enforcement.

As an aside, it’s worth reading the Border Timbers judgments alongside the decision in CC/Devas v India, in which Sir William Blair concluded that ratification of the New York Convention is not a waiver of state immunity (not least because, whilst the ICSID Convention necessarily deals with awards to which a Contracting State is a party, this is not true of the New York Convention).