The UK’s deal to cede sovereignty of the Chagos Islands to Mauritius will be met with “outright hostility” by the Trump administration, Nigel Farage has predicted.

The Reform UK leader, a supporter and friend of the incoming US president, told MPs the agreement would put the UK at odds with an important ally.

He added that Donald Trump’s advisers had security concerns, amid claims the deal could boost China’s influence in the region.

But Foreign Office minister Stephen Doughty said he was confident the “full detail” of the arrangement would allay concerns.

It had won backing “across the national security apparatus in the United States”, he added.

Under the deal, the UK will hand over sovereignty of the islands while retaining control over a joint UK-US military base on the island of Diego Garcia, for an “initial period” of 99 years.

The UK government says the accord, which it hopes to ratify next year, will end legal uncertainty over the islands following international rulings backing Mauritian claims to sovereignty.

But the strategic importance of the archipelago, known officially as the British Indian Ocean Territory, has prompted criticism that the agreement will deliver a security boost to China.

A number of US Republicans have attacked the deal, which has been backed by the outgoing Biden government, although Trump himself has not commented publicly on it.

Speaking in the Commons, Farage said the UK would find “outright hostility” to the deal among the next US administration, adding it had been an “enormous mistake” to sign up to it before last week’s presidential election.

He said he knew this because of time he had spent in America in the aftermath of the election, and because he knew the incoming defence secretary, Fox News host Pete Hegseth, “very well”.

He added that Michael Waltz, expected to become Trump’s national security adviser, “has form” on the topic, having written a letter to Biden’s secretary of state Antony Blinken in 2022 during talks under the previous Tory government.

In the letter, published on his website at the time, the Republican congressman warned that China would “take advantage of the resulting vacuum” if the UK handed over sovereignty of the islands.

“Diego Garcia was described to me by a senior Trump adviser as the most important island on the planet, as far as America was concerned,” Farage told MPs.

He said continuing with the deal would put the UK “at conflict with a country without which we would be defenceless”.

Doughty dismissed Farage’s criticism, arguing legal uncertainty over the Chagos Islands threatened the “secure and effective operation” of the base on Diego Garcia.

He added that given previous findings against the UK, a legally binding ruling siding with Mauritian sovereignty claims “seemed inevitable” at some point, creating legal uncertainty over the base that was “not sustainable”.

He said the deal contained measures to prevent foreign presence in the “outer islands”, and had also been welcomed by all parts of “the US system”.

He added the UK was looking forward to working with the Trump administration, saying: “I’m sure that they will being briefed on the full detail of this deal.

“I am confident that the details of this arrangement will allay any concerns.”

Negotiations on a deal began under the previous Conservative government in 2022, but several senior Tories have also spoken out against the deal.

Shadow foreign secretary Dame Priti Patel, who left government two months before negotiations began under Rishi Sunak, said the accord would “give away a key strategic asset” in the Indian Ocean.

Other Tories to have criticised the deal include James Cleverly, who took part in negotiations himself as foreign secretary but has since described Labour’s proposed agreement as “weak”.