Sir Keir Starmer is facing pressure over US ambassador Lord Mandelson, after the emergence of fresh revelations about his links to the late convicted paedophile Jeffrey Epstein.

It comes after US lawmakers released a number of documents, which included a letter in which the Labour peer called Epstein his “best pal”.

In an interview with Harry Cole Saves the West, Lord Mandelson suggested further “embarrassing” exchanges would emerge. The Sun newspaper has reported he allegedly sent supportive messages to Epstein while he was facing charges in 2008.

Lord Mandelson told the BBC: “I relied on assurances of his innocence that turned out later to be horrendously false.”

He added in response to the Sun’s report: “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.”

The Conservatives and some Labour MPs have called for Lord Mandelson to be sacked but the prime minister has stood by the diplomat.

According to the Sun newspaper, Lord Mandelson allegedly told Epstein to “fight for early release” shortly before Epstein was sentenced to 18 months in prison for soliciting prostitution from a person under the age of 18.

Speaking to the Harry Cole earlier, Lord Mandelson admitted he had continued his association with Epstein for “far longer than I should have done”.

At Prime Minister’s Questions on Wednesday, Sir Keir said Lord Mandelson had “repeatedly expressed his deep regret” for his relationship with Epstein, who died in 2019 while awaiting trial on sex trafficking charges.

A senior Trump administration official told the BBC the White House is continuing to work together with Lord Mandelson on a whole range of issues despite the furore surrounding his relationship with Epstein.

Lord Mandelson spent almost an hour with US President Donald Trump in the Oval Office on Tuesday.

Even though both men are under pressure over their previous friendships with Epstein neither of them mentioned it. The president did say that Lord Mandelson was “doing a fantastic job as ambassador”.

But Conservative leader Kemi Badenoch said Lord Mandelson’s position was “untenable”.

In a post on X, Badenoch said Lord Mandelson “needs to be fired now” in response to the Sun’s report about the diplomat’s links to Epstein.

Speaking earlier at PMQs, Badenoch said Lord Mandelson was “mired in scandal”, raising questions over Sir Keir’s “bad judgement”.

Badenoch called for documents relating to background checks on Lord Mandelson ahead of his appointment to be made public.

The Liberal Democrats have also called for an official investigation into the extent to which Lord Mandelson disclosed his previous contacts with Epstein before Sir Keir appointed him US ambassador in December last year.

The prime minister did not detail exactly what he knew about Lord Mandelson’s links to Epstein prior to appointing him, but said he retained confidence in him and he was “playing an important role” in UK-US relations.

He added that a “full due process” was undertaken prior to Lord Mandelson’s appointment.

Some Labour MPs are worried about the impact of the Mandelson row – just days after Angela Rayner was forced to resign as deputy prime minister.

Although the prime minister has backed Lord Mandelson, a number of Labour MPs broke ranks and went public with calls for the ambassador to resign on Wednesday night.

Among them was Richard Burgon, who said Lord Mandelson “should never have been appointed”, and Nadia Whittome, who echoed that view and added it had “long been known that [Lord] Mandelson remained close to Epstein even after he was convicted of sex offences”.

Bell Ribeiro-Addy became the first Labour MP to publicly call for the ambassador to resign on Wednesday, telling the i Paper the revelations were “going to disturb quite a few people”.

The publication of a letter from Lord Mandelson to Epstein has thrown the spotlight on the pair’s relationship.

Released by a committee of US lawmakers on Tuesday, the letter from Mandelson was one of a number of documents in an alleged “birthday book” given to Epstein in 2003 to celebrate his 50th birthday.

Speaking to Harry Cole, the diplomat said it was “very embarrassing” to see the words published but added they were written “over 20 years ago”.

Lord Mandelson said he felt “a tremendous sense of regret” over his friendship with Epstein, and a “tremendous sense of sympathy” for his victims.

He said he never saw wrongdoing at any point while with Epstein.

Asked why he continued his friendship with Epstein, Lord Mandelson said he “fell for his lies”.

“I accepted assurances he had given me about his original indictment, his original criminal case in Florida. Like very many people I took at face value what he said.”

The controversy comes just days before President Trump is due to visit the UK for a state visit.

A senior Trump administration official declined to say whether the White House continued to have confidence in Lord Mandelson, but the official did tell the BBC they were working together on preparations for the state visit, which will celebrate the successes the UK and the US have shared since Trump returned to office.

Lord Mandelson is highly rated in Downing Street because of his ability to work with the Trump administration.

But his past relationship is awkward for the prime minister. A key question will be over Lord Mandelson’s judgement – remaining friends with Epstein after it first emerged he had been investigated.

The difficult questions for the government are likely to continue if, as Lord Mandelson suggests, there are more details to come.

Mandelson’s connection with Epstein had previously been made public. In 2019, an internal report by the bank JP Morgan said Epstein kept “a particularly close relationship with Prince Andrew, the Duke of York and Lord Peter Mandelson, a senior member of the British government”.

Lord Mandelson has been in and out of British politics for four decades. He was instrumental in the New Labour project which saw Tony Blair win the 1997 election with a huge landslide.

He was a minister in different departments in the government until 2010, when Labour lost power and during that time earned a reputation for bouncing back after twice being forced to resign his ministerial positions.

Additional reporting by Sarah Smith, the BBC’s North America editor.