The co-manager for Donald Trump’s presidential election campaign has called Lord Mandelson an “absolute moron” – as the peer was officially announced as the next UK ambassador to the US.

The Labour grandee, who served in Sir Tony Blair and Gordon Brown’s cabinets, will become the UK’s top diplomat in Washington as president-elect Donald Trump returns to the White House in January.

In a post on X, Chris LaCivita linked to an article in The Daily Telegraph which reported on Lord Mandelson describing Mr Trump as “a danger to the world”.

The peer also described Mr Trump as “little short of a white nationalist and racist” during an interview with an Italian journalist in 2019, according to the newspaper.

In the post on X, Mr LaCivita said: “This UK govt is special replace a professional universally respected Ambo with an absolute moron – he should stay home! SAD!”

He added: “Mandelson described Trump as a danger to the world and ‘little short of a white nationalist’.”

It comes as Sir Keir Starmer confirmed the appointment of Lord Mandelson to the post.

The 71-year-old 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, both for our economy and our nation’s security, and to advance our historic alliance with the United States.”

The prime minister said: “The United States is one of our most important allies and as we move into a new chapter in our friendship, Peter will bring unrivalled experience to the role and take our partnership from strength to strength.”

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Sir Keir also thanked outgoing US ambassador Dame Karen Pierce, who will leave the post at the beginning of next year.

“I would also like to thank Dame Karen Pierce for her invaluable service for the last four years, and in particular the wisdom and steadfast support she has given me personally since July,” he said.

“She made history as the first woman to serve as UK ambassador to the US and she has been an outstanding representative of our country abroad. I wish her all the very best in future.”

Lord Mandelson was one of the key architects of New Labour and helped the party return to power in the 1990s.

He served as Sir Tony’s trade secretary and Northern Ireland secretary before standing down as an MP in 2004 to become a European Commissioner.

After Mr Brown awarded him a peerage in 2008 Lord Mandelson returned to government as business secretary.

Sir Keir Starmer has nominated his former top adviser Sue Gray for a life peerage.

Ms Gray, whose report into the partygate scandal contributed to the downfall of former prime minister Boris Johnson, is among several new Labour peerages that have been announced.

The former civil servant left her role as Sir Keir’s chief of staff in October following an internal power struggle in Downing Street.

She was then appointed to a newly created nations and regions position within Number 10, however, it was confirmed in November that she would not be taking up the role.

Back in 2022, Labour unveiled proposals to abolish House of Lords and to replace it with a “reformed upper chamber”.

However, ahead of the general election this year, the plans were scaled back – with Sir Keir instead pledging to remove the 92 hereditary peers and to introduce an age cap of 80.

It is understood Sir Keir has made the nominations in an attempt to tilt the balance towards Labour in the second chamber.

During the 14 years the Conservatives were in power, the number of Tory peers rose to 273 while there are 187 Labour peers, 78 Liberal Democrat peers and 184 crossbenchers, who are not affiliated to any political party.

Other notable names that have been nominated include:

• Carwyn Jones – former first minister of Wales

• Dame Thérèse Coffey – former deputy prime minister

• Toby Young – founder and director of the Free Speech Union, and an associate editor of The Spectator.

• And Thangam Debonnaire – former shadow cabinet minister who lost her seat unexpectedly at the general election

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