The Government has temporarily been banned from concluding its negotiations on the Chagos Islands deal by an injunction granted in the early hours by a High Court judge.
Downing Street insisted the deal is the “right thing” but would not comment on the legal case.
A hearing is expected to take place at 10.30am.
In the injunction granted at 2.25am on Thursday, brought against the Foreign, Commonwealth and Development Office, Mr Justice Goose granted “interim relief” to Bertrice Pompe, who had previously taken steps to bring legal action over the deal.
“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,” Mr Justice Goose said in his order.
It requires the Government to “maintain the jurisdiction of the United Kingdom over the British Indian Ocean Territory until further order”.
According to the order, the judge granted the injunction “upon consideration of the claimant’s application for interim relief made out of court hours” and “upon reading the defendants’ response”.
Prime Minister Sir Keir Starmer had been expected to attend a virtual ceremony alongside representatives from the Mauritian government on Thursday morning to sign off on the deal.
Britain would give up sovereignty of the island territory to Mauritius under the deal, and lease back a crucial military base on the archipelago for 99 years.
A Government spokesperson said: “We do not comment on ongoing legal cases.
“This deal is the right thing to protect the British people and our national security.”
