British Prime Minister Keir Starmer launched a fierce attack on his former US ambassador Peter Mandelson on Thursday, seeking to assuage anger from across British politics, saying he was sorry he had believed his “lies” before appointing him.

Starmer is under huge pressure, including from lawmakers in his own Labour Party, over the decision to make Mandelson Britain’s envoy to Washington in December 2024 when his ties to the late US sex offender Jeffrey Epstein were already known.

Files released by the US Justice Department last week include emails highlighting just how close that relationship was, and also suggested Mandelson had leaked government documents to Epstein, and that Epstein had recorded payments to Mandelson or his then-partner, now husband.

“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,” Starmer said at the outset of a speech in southern England.

Mandelson, a government minister when Labour was previously in power more than 15 years ago, quit his position in parliament’s upper chamber, the House of Lords, on Tuesday over links to Epstein, and is now under police investigation for alleged misconduct in office.

He has said he does not recall having received payments and has not commented publicly on allegations that he leaked documents. He has not responded to messages seeking comment.

Starmer’s opponents and even those in his own party have said the revelations posed major questions about his judgement. With polls suggesting Starmer is already hugely unpopular with the British public, some in his own party say his position is under threat.

“I want to say this (to Epstein’s victims): 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 appointing him,” he said.

Starmer said he wanted to release the vetting advice that he was given when he selected Mandelson for the Washington role, but said he needed to abide by a police request not to do anything that could prejudice an investigation.