Trump campaign adviser calls Lord Mandelson ‘an absolute moron’

In a statement following his appointment, Lord Mandelson said: “We face challenges in Britain, but also big opportunities and it will be a privilege to work with the government to land those opportunities.”

Prime Minister Sir Keir Starmer said he was “delighted” to appoint Lord Mandelson.

“The United States is one of our most important allies and as we move into a new chapter in our friendship,” he said in a statement.

“Peter will bring unrivalled experience to the role and take our partnership from strength to strength.”

Sir Keir also thanked Dame Karen for “her invaluable service for the last four years, and in particular the wisdom and steadfast support she has given me personally since July”.

UK ambassadors are normally career diplomats or civil servants, but Downing Street said choosing a leading Labour politician “shows just how importantly we see our relationship with the Trump administration”.

It comes as senior Conservative MP Sir Iain Duncan Smith challenged the decision.

He called for an investigation to scrutinise Lord Mandelson’s appointment, his background and “whether or not this is reliable or anyway likely to cause offence in the United States”.

“He’s not a diplomatic appointee, he’s a political appointee and political appointees often carry baggage, particularly if they’ve been out of parliament and out of government for some time,” Sir Iain added.