Nigel Farage has said he would be willing to help Peter Mandelson negotiate with the Trump administration, after the Labour grandee was confirmed as Westminster’s new ambassador to the US.

Lord Mandelson has indicated he believes the Reform UK leader, a friend of Donald Trump, could serve as a link between the UK and the Republican president-elect.

But Downing Street would not be drawn on whether Keir Starmer would like the political veteran to work with Farage, saying when asked only that the prime minister had “already started to begin to build a relationship” with Trump.

Farage has previously offered to use his relationship with Trump and his team to act as a bridge between them and Downing Street. He told the Telegraph he would be willing to work with people in Labour if it was in the “national interest”.

“I am no fan of any of the people in the Labour party, but if it is in the national interest I have always thought I could be a useful asset if they want to use that - but if they don’t, more fool them,” the Clacton MP said.

Farage claimed he could help with talks on trade, tariffs, intelligence-sharing and countering terrorism. He said: “I know these people, and in terms of trade, in terms of defence and in terms of intelligence, the US is our most important relationship in the world – forget Brussels.”

He said free trade deal talks were likely to be done sector by sector. “I would help even if it is to the government’s benefit because it is in the national interest. But they are so split they might not want to take up my offer.”

Mandelson will take up the role in early 2025. As a former EU trade commissioner and UK secretary of state for trade, Mandelson’s CV is seen as a strength amid concerns over what the second Trump presidency could mean for the UK, with the Republican politician having pledged to introduce wide-ranging tariffs.

However, the Labour grandee’s past remarks about Trump – who he once described as “little short of a white nationalist and racist” – may yet plague attempts to foster close US-UK relations. At the weekend Foreign Office sources defended Mandelson after a Trump campaign adviser had called him “an absolute moron”.