LORD Peter Mandelson will be Britain’s next ambassador to the United States, Sir Keir Starmer confirmed today.

The Prime Minister’s most controversial senior appointment yet will see the “prince of darkness” become a key link between No 10 and US president-elect Donald Trump.

Communist Party general secretary Robert Griffiths said: “The millions who voted for Labour and ‘change’ last July did not have the resurrection of Peter ‘intensely relaxed about the filthy rich’ Mandelson in mind.

“I suspect his main mission is to stiffen President Trump’s commitment to the Nato-EU-UK military alliance, sweetened by a US-UK trade deal that favours US monopoly corporations.”

Trump has pledged to introduce wide-ranging tariffs on the first day of his new administration on January 20, with experts predicting damaging consequences for Britain’s goods trade with the US.

A Momentum spokeswoman said: “The decision to appoint Peter Mandelson, a close associate of Jeffrey Epstein and someone who is implicated in the worst excesses of New Labour, as US ambassador demonstrates once again the moral and political bankruptcy that has characterised Starmer’s leadership of the Labour Party to date.”

Left MP John McDonnell, currently suspended from Labour, said: “For many reasons associated with Peter Mandelson’s history in and out of political office, many will feel Keir has lost all sense of political judgement on this decision.”

New Transport Secretary Heidi Alexander, however, said Lord Mandelson is a “really good fit” for the role as “an individual of very significant international standing” and an experienced politician.

His trade policy experience, including as an EU trade commissioner, would be “really important” at a time when Trump has threatened to introduce new tariffs, she told Sky News.

She added: “We need someone as the next ambassador to the US who is going to be able to promote our economic and security interests with one of our closest allies, and so I think he is a really good fit for the job.”

In November, Lord Mandelson said that he would be “very interested” in giving advice on trade to whoever got the job.

The former MP for Hartlepool had told the BBC that he was “more in favour of a new relationship rather than a special one” with the US, but that nobody had spoken to him about the job.

More recently he lost out to be the next chancellor of Oxford University to former Conservative leader Lord William Hague.