UK leader Keir Starmer sacked his ambassador in Washington Peter Mandelson on Thursday following"reprehensible" fresh revelations about the diplomat's friendship with sex offender Jeffrey Epstein.

Dubbed the"Prince of Darkness" during his years as a media spin doctor, Mandelson was twice forced to resign from Tony Blair's Labour government in the late 1990s and early 2000s over allegations of misconduct.

His dismissal as US envoy causes a political and diplomatic headache for the British prime minister as he prepares for next week's visit of US President Donald Trump, who is himself facing questions over his ties to Epstein.

It is the second high-profile departure from the UK government in the past week, after Starmer's former deputy Angela Rayner resigned last Friday for underpaying a property tax.

Starmer, meanwhile, is attempting to reboot his increasingly unpopular government.

The prime minister asked top diplomat Yvette Cooper to withdraw Mandelson after emails he wrote to Epstein after he was convicted came to light, her office said.

"The emails show that the depth and extent of Peter Mandelson's relationship with Jeffrey Epstein is materially different from that known at the time of his appointment," it said.

"In particular Peter Mandelson's suggestion that Jeffrey Epstein's first conviction was wrongful and should be challenged is new information.

"In light of that, and mindful of the victims of Epstein's crimes he has been withdrawn as ambassador with immediate effect."

'Fight for release'

The sacking followed The Sun newspaper and Bloomberg reporting that Mandelson sent supportive messages to Epstein while the financier was being investigated in the United States for sexual offences in 2008.

The Labour party grandee sent emails telling Epstein he was following closely and"here whenever you need".

Mandelson also reportedly told Epstein to"fight for early release" shortly before he received an 18-month sentence for admitting procuring a child for prostitution.

"I think the world of you," Mandelson, a former Labour minister and ex-European trade commissioner, wrote the day before Epstein began his sentence.

A spokesman for Starmer said it was"self-evident" the prime minister "found the content of these emails reprehensible".

He denied claims that Starmer had shown poor judgement by appointing Mandelson less than a year ago when it had been publicly known that he had stayed friends with Epstein after his conviction.

"The Prime Minister has taken prompt and decisive action," the spokesman insisted.

Following the newspaper reports, the 71-year-old Mandelson told the BBC that he"relied on assurances of (Epstein's) innocence that turned out later to be horrendously false".

'Best pal'

"His lawyers claimed that it was a shake down of him, a criminal conspiracy. I foolishly relied on their word which I regret to this day," he added.

His position appeared increasingly precarious after one government minister said he was"completely disgusted" by the messages while another said the emails were "really disturbing and sickening".

At least three Labour MPs had publicly urged Starmer to fire Mandelson.

The smooth-talking political veteran had only started in the key diplomatic post earlier this year, tasked with building a close relationship with Trump.

The prime minister said as recently as Wednesday he had confidence in Mandelson, insisting that"due process was followed" ahead of the appointment.

Starmer's initial backing came after it was revealed that Mandelson called Epstein his"best pal" and an "intelligent, sharp-witted man" in a 2003 letter.

The letter was one of many included in a book compiled to mark the now notorious financier's 50th birthday. The contents were published by a US congressional panel investigating Epstein's sex crimes case.

Mandelson told The Sun he regretted"very deeply" associating with Epstein "for far longer than I should have done".