Peter Mandelson, Britain's smooth-talking ambassador to the United States, was sacked on Thursday after his long-term association with convicted sex offender Jeffrey Epstein became a further distraction for under pressure Prime Minister Keir Starmer.

Mandelson, dubbed the "Prince of Darkness" for his behind-the-scenes manoeuvring during the last Labour government, was forced from the most sought-after diplomatic post after his letters and emails to Epstein were published this week.

The 71-year-old, a veteran Labour politician who was key to the party's success under former leader Tony Blair, had come under scrutiny over his relationship with Epstein after a birthday book was released including a letter purportedly from the now ambassador describing Epstein as "my best pal".

Further emails were published in the media showing that Mandelson had advised Epstein to fight for early release when he faced charges over soliciting a minor.

"In light of the additional information in emails written by Peter Mandelson, the prime minister has asked the foreign secretary to withdraw him as ambassador," Britain's foreign ministry 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."

The ministry said the revelation of Mandelson's suggestion that Epstein's first conviction was wrongful and should be challenged was "new information."

On Wednesday, Mandelson said he deeply regretted ever meeting Epstein and that he had carried on that association "for far longer than I should have done" – a statement that seemed to satisfy Starmer who later in parliament gave him his backing. (Reuters)