LONDON — Britain’s planned handover of the Chagos Islands to Mauritius was blocked by a dramatic 11th-hour legal order Thursday.

U.K. Prime Minister Keir Starmer had been expected to attend a virtual signing ceremony to seal months of talks over the Indian Ocean territory, home to a joint U.S.-U.K. airbase at Diego Garcia and one of Britain’s final imperial possessions.

But, in a High Court injunction granted at 2.25 a.m. on Thursday, High Court justice Julian Nicholas Goose granted “interim relief” to Bertrice Pompe, who was born on Diego Garcia and objected to the plan.

Goose said in his order, aimed the U.K. Foreign Office, and seen by the Press Association news agency: “The defendant shall take no conclusive or legally binding step to conclude its negotiations concerning the possible transfer of the British Indian Ocean Territory, also known as the Chagos Archipelago, to a foreign government or bind itself as to the particular terms of any such transfer.”

It added: “The defendant shall in particular not dispose of the territory in whole or in part.

“The defendant is to maintain the jurisdiction of the United Kingdom over the British Indian Ocean Territory until further order.”

A High Court hearing is now expected to take place on Thursday at 10.30 a.m. London time.

A spokesperson for the British government said Thursday morning: “We do not comment on ongoing legal cases. This deal is the right thing to protect the British people and our national security.”