By my reckoning, yesterday will be remembered as perhaps the most difficult of Sir Keir Starmer’s premiership yet, with even close allies telling me they are not sure where it will end.

His admission at Prime Minister’s Questions that he knew of the friendship between Peter Mandelson and Jeffrey Epstein when he appointed him as US ambassador hardened the sentiment of many a Labour MP who was willing to give him the benefit of the doubt.

Insiders tell me that changed when Starmer told the Commons that security vetting had confirmed the continued friendship between Mandelson and Epstein after the financier was jailed for child prostitution offences, leaving MPs furious at the prime minister and his aides for allowing the ex-Labour minister back into the heart of government.

Some MPs consider this an unforgivable lapse of judgement.

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Starmer faced perhaps his toughest PMQs to date. Pic: Reuters

Number 10 has compromised on the release of files relating to Mandelson’s appointment. It will now be for the independent Intelligence and Security Committee, and not the PM’s top civil servant, as was planned, to decide what should be held back in the interests of national security and international relations.

But that Number 10 had to cave to backbenchers – led by Angela Rayner – concerned about a “cover-up” (as the Conservative leader Kemi Badenoch put it) is symbolic of the breakdown of trust.

A tinderbox that could erupt

There were rumours flying around that Morgan McSweeney, Starmer’s chief of staff, was about to resign – as a few MPs publicly called for him to do so over the decision to reinsert Mandelson into government in 2025.

I’d describe the mood in parliament yesterday evening as a tinderbox, with even some of the PM’s allies unsure about whether the situation is about to erupt.

When I asked one senior ally whether there could be a challenge or resignations that could predicate a challenge, there was a long pause.

“Temperatures are running high,” said the figure, acknowledging that when the mood is as it is, and Sir Keir is where he is in the polls, someone moving against him is a risk.

Another senior figure told me many MPs felt deeply compromised over the scandal, including some ministers.

Asked if he could survive, one minister told me: “I don’t think so. Many in the party are beyond upset.”

The Met have launched an investigation into Mandelson. File image: Reuters
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The Met have launched an investigation into Mandelson. File image: Reuters

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As for the No 10 end, there is deep frustration that the government has been blocked by the Metropolitan Police from releasing information about what Mandelson told the PM and others about his relationship with Epstein.

The intention had been to release this information straight away in order to back up what the PM said in the Commons, but Downing Street has been thwarted as it stands.

There is a view that the release would have been helpful because it would have perhaps led to MPs directing their anger at Mandelson.

The PM’s team are in a bind because they want the information out, but they don’t want to do anything that would affect a criminal investigation with the Met.

One option for Downing Street now could be to go back to the Met and see what they can release.

But with their hands tied, and the mood this febrile, the prime minister is in a precarious position as the Mandelson crisis raises MPs’ anger and leadership speculation all over again.