British Prime Minister Keir Starmer will face his party's MPs as he fights for his political survival after the resignation of his top aide over the Peter Mandelson controversy.

Mr Starmer is expected to address a meeting of the Parliamentary Labour Party (PLP) amid anger over his appointment of Mr Mandelson as ambassador to the US despite knowing that his links with Jeffrey Epstein continued after the financier's conviction for child sex offences.

It comes a day after Morgan McSweeney quit as Mr Starmer’s chief of staff, taking "full responsibility" for giving the prime minister advice that resulted in the "wrong" appointment.

But scrutiny of Mr Starmer's own judgment is mounting as critics, including some of his MPs, have highlighted that he made the final decision.

The pressure on his leadership looks unlikely to ease as the UK government prepares for the lengthy process of releasing tens of thousands of emails, messages and documents relating to Mr Mandelson's appointment.

Mr Starmer believes the files will prove Mr Mandelson lied about the extent of his ties to Epstein during his vetting.

The Guardian, citing a well placed source, said they would show the Cabinet Office had warned about the grave reputational risk of handing Mr Mandelson the ambassadorship.

Mr Starmer and Mr McSweeney, blamed by many for pushing for his ally Mr Mandelson to get the coveted ambassadorship, mutually came to the decision that it was the right moment to move on, it is understood.

The prime minister credited his longtime adviser's "dedication, loyalty and leadership" for Labour's 2024 general election win and said he owed him a "debt of gratitude" in a statement that did not mention Mr Mandelson.

Mr McSweeney's deputies, Vidhya Alakeson and Jill Cuthbertson, have been appointed joint acting chiefs of staff.

Labour MP for York Central Rachael Maskell told the Press Association that Mr McSweeney's departure was "a start" but that the prime minister had to "turn away from the factionalism" engendered by his former aide.

"If he hasn't understood the seriousness of the situation, then I think he will find it very difficult to continue," she told BBC Radio 4's The Westminster Hour.

Other Labour MPs on the left of the party, including Brian Leishman, Ian Byrne and Kim Johnson, suggested Mr Starmer should consider following Mr McSweeney out the door.

Two unnamed Cabinet ministers were quoted by The Times as saying Mr Starmer was "weaker" and "could stand down at any moment", a claim Downing Street said was "categorically untrue".

Union chiefs also heaped pressure on the Labour leader, with Fire Brigades Union general secretary Steve Wright saying he should resign.

Maryam Eslamdoust, the general secretary of the Labour-affiliated Transport Salaried Staffs' Association, told The Telegraph: "There's no case for waiting until May, given the scale of defeat we are facing at these critical elections.

"It's time to elect a new leader."

But Mr Starmer’s ally John Slinger said "the last thing the country needs is leadership speculations".

David Blunkett, former home secretary under Tony Blair’s Labour government, warned against "a party acting like ferrets in a sack".

Downing Street remained defiant, insisting the government's policy agenda and commitment to its economic strategy had not changed.

Mr Starmer is also expected to speak to the women's PLP after Prime Minister's Questions on Wednesday and make on camera interventions this week.

He and Mr McSweeney have pinned blame on vetting by the security services for failing to disprove Mr Mandelson's claims that he barely knew the late financier, which were later dramatically debunked by disclosures in the so-called Epstein files.

Officials have been tasked with examining that process as a priority.

Keir Starmer is expected to address a meeting of the Parliamentary Labour Party amid anger over his appointment of Peter Mandelson as US ambassador

\u003Cp\u003EThe prime minister credited Morgan McSweeney\u0027s \u0027dedication\u0027 for Labour\u0027s election win\u003C/p\u003E

\u003Cp\u003EThe UK government is preparing to release files relating to Peter Mandelson\u0027s appointment\u003C/p\u003E