The deal is still subject to the finalisation of a treaty.

Lammy told the Commons Foreign Affairs Committee it was a “good deal” and that it addressed US concerns about the future of the military base on Diego Garcia.

“I’m very, very confident that this is a deal that the Mauritians will see, in a cross-party sense, as a good deal for them,” Lammy said.

Ramgoolam expressed doubts about the agreement after meeting Jonathan Powell, the UK’s national security adviser, on Monday.

Marco Rubio, Trump’s pick for secretary of state, said in October that the deal posed a “serious threat” to US national security by giving the islands to a country allied with China.

Lammy said: “This is incredibly sad. I know and I’m sad that there’s been so much politicking about this.”

He said the agreement was a “very good deal” for “our national security” because it secured the legal basis of the Diego Garcia military base.

“I’m really reassured about that, and I think an incoming [US] administration will be reassured about that, and I’m confident that the Mauritians are still sure about that, despite politicking that we all know goes on,” Lammy added.

Speaking to BBC Newsnight, Farage said the incoming Trump government was “horrified” by the prospect of the deal the UK government had struck “because they know China has extraordinary naval ambitions”.

If the treaty were signed, he added, it would “be a terrible mistake, it would damage very badly our relationship not just with Donald Trump but with America as a whole and make getting any deal on tariffs that much harder”.

Newsnight political editor Nicholas Watt said he had spoken to a government minister at the heart of the deal who rejected claims that there were doubts over the agreement.

“This deal is fine, we are complying with international law,” the minister told him.

Discussing the agreement in the context of current global tensions, Times columnist Matthew Syed told Newsnight: “I think we’re moving closer, potentially, to a major war between the big powers.

“We have proxy wars happening in Europe and in the Middle East and there could be a blockade by China on Taiwan. Military leaders say this is a strategically absolutely crucial part of the world and China’s leading an ever more cohesive axis including Iran, Russia and North Korea.”

Europe, he argued, had been “free-riding” on US defence spending. “We have to be realistic that in that context, with our denuded defence capacity, it is absolutely crucial that we stand with America.”

Details of the treaty’s legal text are being worked out and it is expected to go before Parliament for scrutiny next year.