Sir Keir Starmer has claimed that “had I known then what I know now, I’d have never appointed” Lord Peter Mandelson as his ambassador to the US.

It comes in the Prime Minister’s first comments since sacking him over links to Jeffrey Epstein.

He continued: “What emerged last week were Bloomberg emails which showed that the nature and extent of the relationship that Peter Mandelson had with Epstein was far different to what I had understood to be the position when I appointed him.

“On top of that, what the email showed was he was not only questioning but wanting to challenge the conviction of Epstein at the time that, for me, went and cut across the whole approach that I’ve taken on violence against women and girls for many years, and this Government’s approach.”

Sir Keir admitted he knew about Lord Mandelson’s emails to Jeffrey Epstein when he defended him in the Commons but not the content they contained.

He added: “It was only on Wednesday, early evening, that I knew the contents of the Bloomberg emails.

“It was only very late on Wednesday when Peter Mandelson replied to the questions that have been put to him by Government officials. And it was on that, basically, I took my decision that he should be removed.”

The dismissal decision came after Mandelson’s Wednesday night responses to officials’ queries.

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Labour parliamentarians have voiced doubts about Starmer’s version of events, with one MP insisting the Prime Minister “should have asked questions in detail” about the emails.

Another Labour member described the situation as “death by a thousand cuts” and suggested chief of staff Morgan McSweeney might need to depart.

Andy McDonald, representing Middlesbrough and Thornaby East, characterised party morale as “very low” and called for transparency about the timeline.

MPs will conduct a three-hour emergency discussion on Tuesday following an application from Conservative MP David Davis.

Emily Thornberry’s foreign affairs committee has scheduled hearings with senior civil servants to examine whether appropriate vetting procedures were observed.

The emails revealed Mandelson had encouraged Epstein to “fight for early release” following his 2008 conviction for child prostitution charges.

In the correspondence, Mandelson expressed feeling “hopeless and furious” about the verdict.

Earlier revelations showed Mandelson had referred to Epstein as his “best pal” in a 2003 birthday tribute book and posed in a bathrobe with the financier.