During his visit Sir Keir will hope to influence Trump as he seeks to reach a peace deal between Ukraine and Russia.

Speaking on the plane to the US, Sir Keir told reporters that a deal would not stop Vladimir Putin from invading Ukraine again, unless the US were able to provide security guarantees.

Asked if the US could offer such support, Trump said a proposed deal with Ukraine over access to critical minerals would provide “a backstop”.

“We are a backstop because we will be over there, we will be working in the country,” he said.

Since becoming prime minister, Sir Keir, who had previously been critical of the president, has sought to build a close relationship with Trump.

However, he did feel compelled to contradict the US president when he accused Volodymyr Zelensky of being a dictator.

Asked about his dictator comments, Trump said: “Did I say that? I can’t believe I said that. Next question.”

Pressed over whether he would approve the UK’s potential deal to hand over the Chagos Islands to Mauritius, Trump said: “We’re going to have some discussions about that very soon, and I have a feeling it’s going to work out very well.

“I think we’ll be inclined to go along with your country,”

In an interview after arriving in the US on Wednesday, Foreign Secretary David Lammy said the controversial deal would not go ahead unless the US supported it.

Under the proposal, the UK would cede sovereignty of the Chagos archipelago to Mauritius but would still be able to use one of the islands, Diego Garcia, which includes a UK-US military airbase.