Bertice Pompe (left) and Bernadette Dugasse outside the High Court after an injunction was granted against the Foreign Office - Yui Mok

A High Court judge has temporarily blocked Sir Keir Starmer from handing the Chagos Islands to Mauritius.

The Prime Minister was set to attend a “virtual signing ceremony” with representatives from the Mauritian government to confirm the controversial handover deal.

But a court ruling just before 2.30am on Thursday has now barred the Government from proceeding with the deal pending a further hearing that got underway this morning.

Opponents to the deal branded the delay a “humiliation” for Labour.

Mauritius was blindsided by the 11th-hour intervention and said it was considering the situation as of Thursday morning.

“We have not received any court order, but we heard about a hearing which could lead to a court order,” a senior official in Mauritius told The Telegraph.

“We are assessing the situation and waiting for feedback from London.”

The Ministry of Defence had planned an event to coincide with the expected unveiling of the deal on Thursday morning, with sources telling The Telegraph to expect an announcement concerning “islands quite far away”.

However, it was forced to cancel at the last minute on Thursday morning as the court case emerged.

The legal challenge was brought by Bertrice Pompe, who was born on Chagos and objected to the plan to lease back the US-UK military base at the expense of British taxpayers.

Ms Pompe has previously said the islands should remain under British control.

She wants the right to return to live where she was born after Chagossians were forced to leave the Indian Ocean territory by 1973 to make way for the base.

In a pre-action letter sent to the Foreign Office in March, she said she would face “severe obstacles” as a British citizen who does not hold Mauritian nationality.

These include possible racial discrimination and the loss of the possibility of returning.

Bertrice Pompe said she would face ‘severe obstacles’ as a British citizen who does not hold Mauritian nationality - Bertrice Pompe

The ruling issued by Mr Justice Goose and seen by The Telegraph said: “Pending the final determination of the claim or until further Order, it is Ordered that a stay of action by the Defendant is imposed that:

“a. 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.

“b. 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.”

The matter returned to the High Court this morning, with both the Foreign Office and Ms Pompe in attendance.

The Conservatives welcomed the delay, with Dame Priti Patel, the shadow foreign secretary, saying: “Labour’s Chagos surrender deal is bad for our defence and security interests, bad for British taxpayers and bad for British Chagossians.

“Today’s legal intervention is a humiliation for Keir Starmer and David Lammy.”

Robert Jenrick, a fierce critic of the Chagos deal, praised the campaigners for challenging the Government.

The shadow justice secretary told Sky News: “All power to the group that has brought this legal action. This is a really bad deal, it is a sell-out for British interests.

“You are seeing British sovereign territory being given away to an ally of China and billions of pounds of British taxpayers’ money being spent for the privilege.”

He added: “If there is a way to force Keir Starmer to step back, think twice, then that is a good thing.”

Nigel Farage claimed Sir Keir Starmer was “desperate” to hand over the Chagos Islands to Mauritius as he responded to the court’s order.

The leader of Reform UK posted on X: “Why is Starmer so desperate to give away the islands? There is no legal need, it will cost us approximately £52 billion, and play into the hands of China. Why?”

Sir Keir’s deal to give away the Chagos Islands would give up British sovereignty over the archipelago to Mauritius despite the country having never previously controlled it.

The agreement also involves a 99-year lease to rent back the Diego Garcia military base.

The deal is expected to cost taxpayers around £9 billion and is the first significant loss of British territory since the independence of Hong Kong in 1997.

As well as concerns over its cost, the deal has also prompted security fears because of deepening Mauritian ties with China and Russia.

David Lammy, the Foreign Secretary, defended the deal when it was struck in October, claiming a legally-binding judgment against the UK was “inevitable”.

Mr Lammy also touted it as proof that the UK was committed to upholding international law.

Chagossians protested outside the House of Parliament last October - Kin Cheung

The United Nations has previously called for the islands to be returned, and a UN court ruled Britain’s possession of the overseas territory “unlawful”.

The plan is opposed by the Conservatives and Reform UK. The Liberal Democrats have also indicated they may vote against the “shambolic” deal.

The Foreign Office first drew up plans to negotiate a “Cyprus-style” deal to hand over the Chagos Islands under the previous Conservative government.

These plans were shelved by Grant Shapps, the then defence secretary, and Lord Cameron, the then foreign secretary, before they were revived by Labour.

A Chagossian-led rally outside the Foreign Office and the High Court began at 9am to demand “justice and transparency”.

A spokesman for the Friends of the British Overseas Territories campaign group said: “We welcome Mr Justice Goose’s ruling and continue to call on the UK Government to immediately halt the deal and urgently engage with the Chagossian community in good faith.

“The £9bn deal has drawn criticism from the Chagossian community, who have been shamefully ignored by the UK Government and excluded from the negotiations.

“The British public has also expressed their alarm at the possible consequences for the UK’s national security and conservation efforts.”

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

The Foreign Office was contacted for comment.

Sign up to the Front Page newsletter for free: Your essential guide to the day's agenda from The Telegraph - direct to your inbox seven days a week.