Pompe and Mandarin v Secretary of State: High Court refuses permission in Chagos sovereignty challenge

The Administrative Court has refused permission for judicial review in two linked claims challenging decisions made by the Secretary of State for Foreign, Commonwealth and Development Affairs in connection with the transfer of sovereignty over the British Indian Ocean Territory (BIOT) to Mauritius. Mrs Justice Stacey DBE held that the defendant had delivered a "clear knockout blow" to each ground of challenge.

The claims were brought by Bertrice Pompe (AC-2025-LON-001642) and by Louis Michel Mandarin and his son Louis Misley Mandarin (AC-2025-LON-002073), all British citizens and self-identifying Chagossians. The Treaty between the United Kingdom and the Republic of Mauritius, providing for Mauritian sovereignty over the Chagos Archipelago, was signed on 22 May 2025 and is presently before Parliament as a Bill.

Six grounds of review were advanced: failure to consult the Chagossian community; Wednesbury irrationality; breach of the Public Sector Equality Duty (PSED) under section 149 of the Equality Act 2010; unlawful discrimination contrary to Article 14 ECHR; procedural unfairness; and breach of Article 8 ECHR.

Justiciability and the foreign relations prerogative

The court accepted the defendant's primary submission that the claims amounted, in substance, to a direct challenge to the exercise of the treaty-making prerogative. The grounds were found to be "inextricably intertwined" with high-level foreign policy considerations — including defence, security, and international relations — attracting an especially broad margin of discretion. Citing Miller [2017] UKSC 5 and Rahmatullah (No. 2) [2017] UKSC 1, the court held this alone was fatal.

Consultation and procedural fairness

On Ground 1, the court found no obligation to consult had arisen. Ministerial statements expressing an intention to "engage" with Chagossian communities did not amount to the clear and unambiguous promise required to establish a legitimate expectation, applying Secretary of State for Work and Pensions v Everleigh [2023] EWCA Civ 810. Prior consultation exercises — conducted in connection with the Marine Protected Area in 2009 and the resettlement review in 2015–16 — concerned different subject matter and could not establish a settled practice requiring consultation on sovereignty. Crucially, the Treaty did not deprive the claimants of any rights they currently held, given Chagossians have never enjoyed a right of abode in the BIOT.

Ground 5, procedural fairness, failed on similar reasoning. The engagement exercises conducted by the defendant were held sufficient, and the issue had in any event been determined against the claimants in R (Hoareau and Bancoult (No. 5)) v Secretary of State [2019] EWCA Civ 1010.

PSED and ECHR grounds

The PSED claim (Ground 3) was dismissed on the basis that section 149 does not apply to decisions given effect by primary legislation, and paragraph 14 of Schedule 18 to the Equality Act 2010 expressly excludes the preparation and promotion of an Act of Parliament from its scope, following R (Adiatu) v HM Treasury [2020] EWHC 1554 (Admin).

Grounds 4 and 6 — Articles 14 and 8 — were held unarguable. The claimants had no rights of abode in the Islands that were being interfered with; the complaint was not of rights taken away but of rights never held. Article 14 was parasitic on a substantive Convention right and no adequate foundation for engagement with those rights was established.

Permission was refused on all grounds. The application for a costs-capping order did not fall to be considered.

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