The High Court in London has refused permission for a legal challenge seeking to overturn the United Kingdom’s agreement with Mauritius on the future of the Chagos Archipelago, dealing a fresh blow to Chagossian campaigners who say they were sidelined in the negotiations.

The claim was brought by three plaintiffs, among them Bertrice Pompe, a British national born on Diego Garcia, the largest island in the Chagos chain and host to a major United States military base. The claimants argued that the Foreign, Commonwealth and Development Office failed to consult Chagossians before concluding the sovereignty agreement with Mauritius, despite the community’s direct stake in the islands’ future.

In a written ruling, Judge Mary Stacey accepted that the Chagossians had suffered what she described as a long and shameful history of treatment at the hands of the British state. In the late 1960s and early 1970s, the entire population of the archipelago was forcibly removed so that the UK and the US could establish military facilities on Diego Garcia. Many of those expelled and their descendants have since lived in exile in Mauritius, the Seychelles and the United Kingdom, often in precarious conditions.

Despite that acknowledgment, the judge concluded that the new challenge largely repeated arguments that had already been tested and rejected in earlier litigation over the Chagos Islands. On that basis, she refused permission for the case to proceed, effectively closing this particular avenue for contesting the UK Mauritius accord.

Britain retained control of the Chagos Islands after granting independence to Mauritius, detaching the archipelago to form the British Indian Ocean Territory. That move has been condemned in international forums, including by the International Court of Justice and the United Nations General Assembly, which have called on the UK to end its administration of the territory.

Under the recent agreement, the UK has committed in principle to transfer sovereignty over the Chagos Archipelago to Mauritius while preserving the long standing defence arrangements on Diego Garcia through a continued lease for the military base. For many Chagossians, however, the central question remains unresolved: whether they will be allowed a meaningful right of return and adequate reparations for decades of displacement.