It was immediately clear, however, that Downing Street had already anticipated the significant backlash that the decision would provoke.

Just over 40 minutes later the Foreign Office sent journalists an email directing them to a statement by Joe Biden.

No 10 had called in the cavalry with the US president immediately dismissing speculation that the handover would prompt US ire.

“It is a clear demonstration that through diplomacy and partnership, countries can overcome long-standing historical challenges to reach peaceful and mutually beneficial outcomes,” the White House said.

“This agreement affirms Mauritian sovereignty over the Chagos Archipelago, while granting the United Kingdom the authority to exercise the sovereign rights of Mauritius with respect to Diego Garcia.”

A few hours later another statement dropped from Anthony Blinken, the US secretary of state, who said the deal “reflects the power of diplomacy to solve longstanding challenges”.

But by that point the furious response to the announcement was already underway, with Boris Johnson leading the charge.

In an interview with The Telegraph, the former prime minister branded the decision “feeble” and said it would weaken Britain’s standing in the world.

Raising his voice, he said: “No, no! I mean, God, that’s another, I mean, what’s he doing?

“The Chagos Islands are a vital national asset. And have you seen how far away Mauritius is from the Chagos islands? I have, and it’s ridiculous.

“It’s absolutely ridiculous. But this is what they’re like. They are lefty lawyers from Doughty Street and Matrix chambers. They always think their own country is in the wrong.

“You don’t buy any influence by doing this. It’s a sort of delusion that the world thinks better of you for doing this. They don’t, they think you’re feeble.”

Sir Iain Duncan Smith, a former Tory leader who has been sanctioned by China, also described the agreement as “astonishing”.

“At the heart of this lies the real threat from China and we have a government of Mauritius that is very pro-China,” he said.

“If China gets involved with Mauritius, I cannot see how you can continue to use that place as it is now or how the Americans can either.”

‘A dangerous capitulation’

All four Tory leadership candidates also quickly began jostling to spearhead the opposition.

Robert Jenrick, the former immigration minister and race frontrunner, said: “It’s taken three months for Starmer to surrender Britain’s strategic interests.

“This is a dangerous capitulation that will hand our territory to an ally of Beijing.”

Mauritius and China struck a free trade agreement in 2021 – the first of its kind between Beijing and an African country – leading to a large rise in trade.

Mr Jenrick’s condemnation was echoed by Kemi Badenoch, who added: “Anyone who has been paying attention to the geopolitical climate will understand the strategic necessity of these islands.

“Labour has either not been paying attention or don’t care. Either way, this decision weakens UK influence across the world.”

While it may appear to be the most unifying of issues, it sparked conflict between two of the leadership camps.

When James Cleverly, the shadow home secretary, branded the decision as “weak, weak, weak”, his rival Tom Tugendhat pointed out that it was Mr Cleverly who, as foreign secretary, oversaw the drawing up of much of the deal that Labour has enacted.

Mr Tugendhat said: “This deal not only threatens our security but also undermines our allies, opening the possibility of China gaining a military foothold in the Indian Ocean.

“It compromises both our national security and the stability of the region.”

But if Sir Keir took some pleasure at seeing the Tories scrap, criticism from Labour MPs of the deal will have also given him some cause for concern.

Peter Lamb, the MP for Crawley, said it was “very disappointing” that the islands had been handed over without the consent of the displaced Chagossian people, many of whom live in his constituency.

Posting on social media, he said: “The decision over the future of the islands belongs the Chagossian people, it’s not for the UK to bargain away. Sixty years on from their exile, they’ve been let down again.”