Sir Keir Starmer has sparked fears over the futures of Gibraltar and the Falklands after giving away the Chagos Islands.

The Prime Minister’s decision to authorise the handover of the strategic archipelago to Mauritius was condemned as “utterly shameful”.

Downing Street announced it was ending 200 years of British rule by ceding sovereignty of the territory, which hosts the Diego Garcia airbase that the UK operates with the US.

The territory will come under Mauritius’s jurisdiction despite concerns over its closeness to China, with whom it signed an unprecedented trade deal in 2021.

The move, just three months into Labour’s time in government, has prompted fears over Sir Keir’s approach to other British Overseas Territories, including from two former defence secretaries.

Grant Shapps said: “The decision by Starmer to give up the British Indian Overseas Territory proves he cannot be trusted to protect British interests.

“We are lucky that Starmer wasn’t in charge when Argentina invaded the Falklands, he would have handed them over on a silver platter.”

Penny Mordaunt said the decision was “massively detrimental to the UK’s interests” adding it was “utterly shameful it’s been done in recess”.

She said: “This is what happens when a new government has no clue. Some official tells them it’s a good idea and they agree to this with no understanding of the ramifications.”

‘An open wound’

Tory leadership candidates also raised concerns, with Tom Tugendhat writing in The Telegraph: “Will the buck stop with surrendering Chagos?…  Argentina has long sought to wrestle the Falklands from us; whilst Gibraltar is an open wound in our relations with Spain.”

A source involved in negotiations under the Tory government said the decision was “utterly mad”.

“Gibraltar negotiations are still going on,” they said. “If they do the same, this model would mean joint sovereignty over the airport in Gibraltar in Spain which would be a disaster.

“And the idea of admitting wrongdoing, or putting to bed past wrongdoing, is essentially the Argentine stance over the Falklands.”

The governments of Gibraltar and the Falklands both issued statements insisting that they were not concerned about the decision because their own populations had overwhelmingly voted to remain British.

Argentina promises ‘concrete action’ to regain Falklands

On Thursday night Argentina vowed to gain “full sovereignty” of the Falkland Islands following the Chagos decision.

The country’s foreign minister, Diana Mondino, welcomed the step taken towards ending “outdated practices”.

She promised “concrete action” to ensure that the Falklands – the British-controlled archipelago that Argentina calls the Malvinas and claims as its own – are handed to Buenos Aires.

In an intervention that will fuel rising criticism of the Mauritius agreement, Ms Mondino said: “The long dispute between Britain and Mauritius came to a conclusion today, with Mauritians successfully regaining their territory of Chagos.

“Following the path we have already taken, with concrete actions and not empty rhetoric, we will recover full sovereignty over our Malvinas Islands.

‘Unique agreement’

A Foreign Office spokesman said: “The situations are not comparable. This is a unique agreement that has absolutely no bearing on the wider UK government policy regarding our other Overseas Territories. It is a very different issue with a very different history. We remain committed to our Overseas Territories family.

Sources said the Government had delivered an agreement which means for the first time in over 50 years, the base will be undisputed and legally secure with full Mauritian backing. They said the operation of the base will continue unchanged.

David Lammy announced on Thursday that a deal had been struck which is expected to see the islands handed over to Mauritius next year.

He insisted that under the agreement Britain will be guaranteed control over Diego Garcia, which is used by the US military, for at least a century.

‘Vital military base’

The Foreign Secretary said the pact was necessary because a series of international legal defeats had thrown the future of the base into doubt.

“Today’s agreement secures this vital military base for the future,” he said.

“It will strengthen our role in safeguarding global security, shut down any possibility of the Indian Ocean being used as a dangerous illegal migration route to the UK, as well as guaranteeing our long-term relationship with Mauritius, a close Commonwealth partner.”

Mauritius, which is 1,400 miles from the Chagos Islands and never owned them, has brought repeated claims of sovereignty over recent decades.

It won a landmark case at the International Court of Justice in 2019, which issued a non-binding judgment ordering Britain to hand them over.

A deal for the handover was drafted under the Tories but then kiboshed by Lord Cameron, who was worried about the security implications.

The former foreign secretary was concerned by the influence that China is said to wield over the Mauritian government. Officials said the 2021 agreement would form the basis of “enhanced collaboration” between the nations.

Matthew Miller, the US State Department’s spokesman, said on Thursday night that he is “fully confident” the security of the base is protected by the agreement.

Nigel Farage, the leader of Reform UK, criticised the handover, saying: “Our American allies will be furious and Beijing delighted.”

The US reportedly raised concerns over the handover, with one official telling The Times: “They were saying that we would rather that you didn’t do this as it would make things very complicated for us. But we understand this is a matter for you to resolve.”

However, Joe Biden, the US president, insisted that he welcomed the move.

He said in a statement: “The agreement secures the effective operation of the joint facility on Diego Garcia into the next century.”