The US State Department is to “imminently” write to Prime Minister Keir Starmer and the Foreign Office as part of a major intervention on the Chagos Island deal, GB News understands.

Robert Midgley from Friends of the British Overseas Territories told The Late Show Live an official communication would soon hit the desk of the Prime Minister outlining an official change in the US position.

The islands in the Indian Ocean, which host a UK-US military base on the largest island of Diego Garcia, will be handed over to Mauritius under the deal.

Britain will lease back the military base on the island of Diego Garcia, which is jointly used with the US, for at least 99 years, while making payments to Mauritius.

Secretary of State Marco Rubio initially suggested the US backed the agreement, but two weeks ago the President appeared to signal a change of heart on social media, describing the deal as an “act of great stupidity”.

He said: “Shockingly, our ‘brilliant’ Nato ally, the United Kingdom, is currently planning to give away the Island of Diego Garcia, the site of a vital US Military Base, to Mauritius, and to do so for no reason whatsoever.

“There is no doubt that China and Russia have noticed this act of total weakness.”

He added: “The UK giving away extremely important land is an act of great stupidity, and is another in a very long line of National Security reasons why Greenland has to be acquired.”

Referring to Mr Trump’s comments, Mr Midgley told GB News: “The UK hasn’t taken that seriously enough.

“What they have been taken seriously enough is Marco Rubio’s post for May 2025, so they keep referring it back.”

“No10 is definitely spinning right now,” Mr Midgley added.

Friends of the British Overseas Territories have been in Washington this week, seeking answers on the official US position on the Chaos deal.

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After meeting with officials in the State Department on Friday, Mr Midgley said: “They will be imminently writing officially to the FCDO [Foreign, Commonwealth and Development Office] to confirm their new policy stance towards the Chagos Islands, which will be following Donald Trump’s stance from Truth Social.”

UK ministers had repeatedly said the Chagos deal would only go ahead if it had the support of America.

Legislation to officially implement the agreement between the UK and Mauritian governments is currently in its final stages.

The Bill is currently in “ping pong”, where legislation is batted back and forth between the Commons and Lords until agreement is reached between the Houses.

The delay in the latest round came after the Conservatives tabled an amendment calling for a pause “in the light of the changing geopolitical circumstances”.

Earlier this month the Prime Minister’s official spokesman said the UK Government’s position on Chagos “remains unchanged”.

“This deal secures the operations of the joint US-UK base for generations. It has robust provisions for keeping its unique capabilities intact and our adversaries out,” he said.

“As the world grows more dangerous, so too does the importance of the base for our national security.

“It’s one of the most significant contributions to the UK and US intelligence and security relationship, and almost every operation from the base is in partnership with the US.”