At an address to the party faithful in London, Starmer had made an impassioned plea to both his party and voters to stick with him and avoid a leadership contest he said would only bring chaos, promising to be bolder.
But his speech, in which he all but admitted he had been too timid in tackling the myriad of problems besetting the United Kingdom since he won a large majority in 2024, did little to ease the anger felt over one of the worst defeats for Labour in last week's local elections.
Four ministerial aides said they were resigning, believing that Starmer, 63, was not the man to lead Labour into the next general election, due in 2029, and hoping to trigger a leadership contest that could last weeks if not months.
"It is clear to me that the prime minister has lost authority not just within the parliamentary Labour Party but across the country and that he will not be able to regain it," said Tom Rutland, a ministerial aide to the environment minister, in his resignation letter.
Catherine West, an Australian-born former junior minister who broke cover at the weekend to threaten to seek a leadership contest if Starmer failed to offer radical change, told Reuters she had received 80 responses supporting her demand that the prime minister set out a timetable for his departure.
She called for a leadership election to happen in September.
The Times newspaper reported on Monday evening that Starmer had been told by interior minister Shabana Mahmood and other senior cabinet ministers to consider setting out a timeline for his departure.
The Times reported that Mahmood was one of at least three cabinet ministers to suggest that the prime minister needs to consider his position.
Two of Starmer's closest allies, environment minister Steve Reed and defence minister John Healey, entered the prime minister's Downing Street office late on Monday, according to Sky News.
Officials did not respond to a request for comment on whether it was a scheduled meeting.
Earlier, Starmer had tried to change the narrative about his leadership, arguing that he would now offer a "complete break" with the decision-making of the past that led to the "status quo".
Starmer promised to govern with the "hope" and "urgency" required to improve living standards and produce a "stronger, fairer" country to try to crush the challenge posed by the populist Reform UK party on the right, and the Greens from the left before the next general election.
"Our response this time must be different, a complete break. We must make this country stronger and take control of our economic security," Starmer said earlier on Monday.
"I know that people are frustrated by the state of Britain. Frustrated by politics, and some people are frustrated with me," he said.
"I know I have my doubters and I know I need to prove them wrong. And I will," Starmer told an audience of party faithful, who offered him several standing ovations.
The applause was a long way from the messaging groups of Labour MPs, where talk about removing Starmer has stepped up a gear after the party lost hundreds of seats in elections to councils in England and the parliaments in Scotland and Wales.
While there were few Labour MPs who were prepared to publicly endorse Starmer, the prime minister's closest allies again warned against removing a leader this early into his term, saying it would only further harm the UK.
"Changing leader just leads to chaos. We saw what happened under the Tories. Let's learn from their mistakes, not repeat them," Reed said on social media, referring to the opposition Conservative party.
