Keir Starmer pledged to press on with his agenda as the departure of a second senior aide in 24 hours left the U.K. prime minister’s grip on power appearing increasingly tenuous.

The resignation of Starmer’s communications director, Tim Allan, on Monday, after just five months on the job will feed the sense of crisis engulfing 10 Downing St. The prime minister was already reeling from the departure on Sunday of his chief of staff, Morgan McSweeney, a key architect of the Labour Party’s landslide election win 18 months ago.

In his remarks to staffers in No. 10, Starmer praised McSweeney’s contribution to Labour’s political revival in recent years and signaled that he intended to fight on as prime minister.

“We must prove that politics can be a force for good. I believe it can. I believe it is,” Starmer said, according to a statement. “We go forward from here. We go with confidence as we continue changing the country.”

Starmer is also due to address members of parliamentary Labour Party later on Monday. His spokesman, Tom Wells, told reporters the prime minister wasn’t planning to resign.

The renewed speculation over Starmer’s position knocked long-maturity gilts and the pound early on Monday. Yields on 10-year government bonds rose as much as five basis points to 4.57%, before paring the move to 4.55%. The pound weakened as much as 0.5% to 87.3 pence per euro.

Investors have tended to react negatively to the prospect of Starmer or Chancellor of the Exchequer Rachel Reeves leaving their posts, out of concern they could be replaced by colleagues more willing boost spending.

Starmer, who has been struggling with historically low approval ratings and faced rebellions by backbench Members of Parliament, has come under fire over his decision in late 2024 to appoint Labour grandee Peter Mandelson as ambassador to the U.S. That decision is being reexamined after the extent of Mandelson’s relationship with convicted sex offender Jeffrey Epstein was revealed in files released by the U.S. Justice Department late last month.

While McSweeney took the blame for Mandelson’s appointment in his resignation statement, the decision ultimately rested with Starmer. The criticism has fueled questions about Starmer’s ability to hang on as prime minister, with his leadership already weakened by series of policy reversals and the rise of Nigel Farage’s populist Reform U.K. in the polls.

No. 10 officials were bracing for Cabinet ministers to privately tell the premier to stand aside or threaten their resignations if he doesn’t, according to people familiar with the matter who spoke anonymously in order to be candid about the turmoil at the top of the Labour Party. One aide to a Cabinet minister said it was 50-50 whether Starmer would last the week.

Allan’s exit will leave another void inside Starmer’s depleted brain trust. McSweeney and Allan had been locked in a power struggle and aides risked descending into open infighting, according to people familiar with the matter.

“I have decided to stand down to allow a new No. 10 team to be built,” Allan said in a statement on Monday morning. “I wish the PM and his team every success.”

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—With assistance from Greg Ritchie, Joe Mayes and Alex Morales.

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