The fate of prime minister Keir Starmer dominates the UK front pages on Monday after his embattled chief of staff, Morgan McSweeney, resigned over the appointment of Peter Mandelson as ambassador to Washington.

In standing down, McSweeney admitted the decision to advise sending Mandelson to the US despite his links to convicted sex offender Jeffrey Epstein “was wrong”. “I advised the prime minister to make that appointment and I take full responsibility for that advice,” he said, after a Sunday phone call with Starmer.

“Starmer fights to regain control over party after McSweeney exit” is how the Guardian framed Starmer’s predicament. Senior Labour sources said McSweeney’s departure left the prime minister dangerously exposed as he headed towards a series of policy and electoral challenges – including the Gorton and Denton byelection.

The Telegraph splashed on “Starmer plays his last card as McSweeney leaves No10”. Its report said the departure of Starmer’s chief of staff will not be enough to save the prime minister’s premiership. “Morgan has taken responsibility for the advice. But there were plenty of others pushing for it,” an unnamed Labour source said.

“So how long can Starmer cling on?” the Mail asked. Brian Leishman, the Labour MP for Alloa and Grangemouth, said “there must be a change in political direction and that comes from the very top”, and the paper said rivals including Angela Rayner and Wes Streeting were jockeying for position in a potential leadership contest.

The Mirror simply said “Blame me” of McSweeney falling on his sword, and described the moment as a “Labour leadership crisis”. Vidhya Alakeson and Jill Cuthbertson, who were McSweeney’s deputies, have reportedly been appointed as acting chiefs of staff, it said.

“PM’s top aide quits over support for Mandelson” was the lead story for the Times, which said Starmer had “sacrificed his closest political ally”. An unnamed cabinet minister pondered a potential abrupt exit for Starmer, too: “We’re asking the question of whether he will be there at the end of the week. There’s a feeling he could stand down at any moment. The next 48 hours is going to be crucial.”

Top story at the FT said “Starmer battles to save premiership after top aide McSweeney steps down”, and it reported that the prime minister now faces a difficult period of intense scrutiny from inside and outside the party. “Keir Starmer has to take responsibility for his own terrible decisions,” Conservative leader Kemi Badenoch said.

“Operation save Starmer: No 10 chief forced out to buy PM time” was the i paper splash. Its report said McSweeney’s resignation might calm some nerves inside the Labour, while others described Starmer as “fatally wounded … a dead man walking”.

The Express posed the question that will dominate talk around Westminster on Monday: “Are Starmer’s days numbered as key aide resigns?”