Keir Starmer is under intense pressure over the appointment after newly released documents revealed new details of Mandelson's close relationship with Epstein.
British Prime Minister Keir Starmer apologised on Thursday to victims of Jeffrey Epstein for appointing Peter Mandelson as the UK's ambassador to Washington despite his ties to the disgraced financier.
The prime minister said Mandelson had lied and "portrayed Epstein as someone he barely knew."
To the victims, he said: "I am sorry, sorry for what was done to you, sorry that so many people with power failed you. Sorry for having believed Mandelson's lies and appointed him and sorry that even now you're forced to watch this story unfold in public once again."
Starmer appointed Mandelson, a veteran politician, as ambassador to the US in 2024.
The prime minister fired him in September after emails were published showing that he maintained a friendship with Epstein following the late financier's 2008 conviction for sex offenses involving a minor.
Epstein died by suicide in a jail cell in 2019, while awaiting trial on US federal charges accusing him of sexually abusing dozens of girls.
Starmer never met Epstein and is not accused of any wrongdoing. But the prime minister is under intense pressure over the appointment after newly released documents revealed fresh details of Mandelson's close relationship with Epstein.
"I was lied to," Starmer said.
"It had been publicly known for some time that Mandelson knew Epstein, but none of us knew the depth and the darkness of that relationship."
British police are investigating Mandelson over potential misconduct in public office. He is not accused of any sexual offenses.
Documents published last week by the US Department of Justice contain new revelations, including papers suggesting Mandelson shared sensitive government information with Epstein after the 2008 global financial crisis.
There are also scores of chatty, jokey messages pointing to a much closer relationship than Mandelson had previously disclosed.
The newly released files also suggest that in 2003 to 2004, Epstein sent three payments totaling $US75,000 ($107,000) to accounts linked to Mandelson or his partner Reinaldo Avila da Silva, now his husband.
Mandelson, 72, has been a major, and contentious, figure in the Labour Party since the 1990s.
He twice had to resign from senior posts in previous administrations because of scandals over money or ethics.
He was chosen as ambassador because his trade expertise, network of contents and mastery of the political "dark arts" were considered assets in dealing with President Donald Trump's administration.
Critics say Mandelson's ties with Epstein made his appointment too risky and Starmer was, at best, naive.
"I think the prime minister has shown that his judgment is questionable," Labour lawmaker Paula Barker said.
"I think he has questions to answer. I think he has a very long way to go to rebuild trust and confidence with the public, and trust and confidence within our party."
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