A backbench Labour MP seeking to trigger a leadership challenge to Sir Keir Starmer has told the BBC the party needs to "move quickly" to replace him after suffering heavy election losses.
North London MP Catherine West has urged cabinet ministers to challenge the prime minister, and has threatened to do so herself if they do not.
It comes as more Labour MPs went public with calls for Sir Keir to go, including his former ally Josh Simons, who said the PM had "lost the country".
Education Secretary Bridget Phillipson rallied behind Sir Keir, who is planning to make a major speech on Monday in a bid to shore up his premiership, in an interview on the BBC's Laura Kuenssberg programme.
Addressing fellow guest West directly, Phillipson said: "I love you dearly Catherine, but we just disagree on this one".
The senior minister acknowledged Labour had taken "a real kicking" from voters in Thursday's elections and that the party needed to "tell a better story".
She said the PM would set out a "fresh direction for our country and for our party" in his speech on Monday.
Asked if he would still be party leader at the time of the next general election, which will come in 2029 at the latest, Phillipson said: "Yes, I do believe that."
She conceded that voters did not feel the Labour government had "delivered" on the change it promised in the 2024 general election but insisted that "fighting amongst ourselves" in a leadership contest was not the answer.
It comes after Labour lost almost 1,500 councillors in England, mainly to Reform UK and the Greens, and was kicked out of power in Wales. Labour came joint second in Scotland, where the SNP retained control of the Parliament.
West, a former junior minister, is not bidding to be the next Labour leader and prime minister herself, but by triggering a leadership contest she would be aiming to flush out heavyweight contenders she thinks could do a better job than Sir Keir.
To secure a leadership contest, she would have to be endorsed by 81 Labour MPs, a fifth of the current total. She said she had 10 backers so far.
More than 30 Labour MPs have publicly called for the prime minister to resign or to set out a timetable for his departure.
West told the BBC: "I will hear what the prime minister's got to say tomorrow and, then if I'm still dissatisfied, I will put out my email to the Parliamentary Labour Party, asking for names.
"And the reason I'm doing that is not for me. It's for working people, because Labour is the only party that can beat Reform."
She added: "We have a problem, we have to move quickly to fix it, because otherwise it will lead to uncertainty".
Asked if she could gather enough names to start a contest, the Hornsey and Friern Barnet MP said: "We will find out when I put out my email to the Parliamentary Labour Party."
Sharon Graham, leader of the Unite union, said she was "very sure" that the prime minister would not lead Labour into the next election.
Nadine Dorries, a former Conservative minister who switched to Reform, said Sir Keir was an "asset" to her new party.
"We'd love Starmer to stay there" she said but added: "For the sake of the country... Labour should change their leader."
Health Secretary Wes Streeting, former deputy prime minister Angela Rayner and Greater Manchester Mayor Andy Burnham are thought to be the main potential challengers to Sir Keir's leadership.
Burnham cannot enter a contest without first becoming an MP and earlier this year, he was blocked by the party's ruling body from standing in the Gorton and Denton by-election.
The mayor's supporters are hoping a leadership contest can be delayed until he is able to return to Parliament.
On Sunday, Josh Simons and Anna Dixon became the latest Labour MPs to urge the prime minister to step down.
Simons was a senior figure in Labour Together - the organisation that helped Sir Keir win the Labour leadership - and was until last month a minister.
Writing in The Times, he said: "I do not believe the prime minister can rise to this moment. He has lost the country. He should take control of the situation by overseeing an orderly transition to a new prime minister."
Dixon, MP for Shipley, told BBC Politics North: "I don't believe that the public any longer have confidence that the prime minister can take us successfully into the next set of elections".
She said she thought the prime minister was a "good man" but needed to "take control of this... and plan for an orderly transition in our leadership".
Liberal Democrat leader Sir Ed Davey said this week's elections had been a verdict on the prime minister's "failure to tackle the cost-of-living crisis".
He argued that building a closer relationship with the EU was "the best way to deliver the economic growth that this country desperately needs" but that Sir Keir's plans were "too weak and unambitious".
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