Wes Streeting is preparing to launch a leadership challenge against Keir Starmer on Thursday if the health secretary can secure the support of enough MPs to trigger a contest.

Streeting’s move to force a race has sparked a frantic scramble on the left of Labour to find a candidate to oppose him, with Ed Miliband and Angela Rayner both possible contenders.

The health secretary, who is considered to be on the Blairite right of the party, has been organising an attempt to oust the prime minister for days since Labour’s disastrous election results, despite his friends insisting he did not want to make the first move.

Andy Burnham, the Greater Manchester mayor, is the favoured replacement for Starmer by many on the soft left, but does not yet have a seat despite trying to persuade several MPs to stand down for him. His latest hopes are said to be Afzal Khan or Jeff Smith, both Manchester MPs, although their friends denied it. If they were to step aside, it would be difficult for Burnham to fight a byelection and enter parliament in time for any leadership contest.

With Labour on the brink of civil war, Keir Starmer was calling ministers and MPs into his office in parliament to plead with them not to allow a competition to be triggered. He told MPs that “we can’t let a leadership contest plunge us into chaos” and that a “challenge would 100% do that”.

His cabinet allies, including Rachel Reeves, were also in the tea rooms of the House of Commons urging MPs to consider that a leadership election would paralyse the ability of the government to get things done.

Streeting was on Wednesday still working on getting the necessary 81 names to support his bid for the top job, with his outriders telling MPs that a contest was definitely on. The idea that Starmer had seen off a putsch was “laughable”, one added.

“No one has the numbers till the bell is struck, even canvassing isn’t real, people need certainty before they write their name down. But he thinks he’s got the numbers,” they said.

A second MP, also close to the Streeting camp, said they had been involved in discussions about getting the requisite numbers he would need to trigger a contest, and had begun ringing round MPs.

Two other MPs said they had been called by allies of Streeting on Tuesday evening to tell them: “He’s going for it.” Streeting is also known to have been calling MPs directly including some supporters of other candidates who were surprised to be rung.

Some of his opponents were still sceptical that he had the numbers, given that many of those who have called on Starmer to go so far are from the left of the party. Streeting had a brief 16 minute coffee meeting with Starmer on Wednesday, with neither side revealing what had been said.

Allies of Miliband, the energy secretary, said they believe he also has the required backing among MPs, while Rayner could also launch her own bid – although sources said she is still not dead set on being the left’s candidate.

Downing Street has insisted that Starmer would fight any challenge from Streeting and other candidates, having just set out a programme for government in the king’s speech that contains 30 new bills.

However, Starmer supporters were also hinting that Downing Street may increasingly be coming round to the idea that they could drop opposition to Burnham becoming an MP later in the parliament.

His closest friends say that if the polls still show Labour is floundering on 15% in the polls in May 2028 and Burnham’s term in Greater Manchester is at an end, then an accommodation may be reached that Starmer will stand down.

One cabinet minister supporter of Starmer said: “If you get to the point, closer to the election, where he can’t win the election but somebody else could …. if he reaches a point that he’s clear in his own mind that it can’t be done then he’d make sure there was an orderly transition. But he’s not there yet.”

However, other cabinet ministers have been telling Starmer that he should not fight a contest while still in office, and that it would have been better to set a timetable for his resignation.

One senior Labour source pointed to Starmer’s missteps in dealing with the crisis as a reason why he should not contest a challenge, highlighting his interview from over the weekend suggesting he wanted to stay in power for 10 years and decision to bring back Gordon Brown and Harriet Harman to refresh his government.

If Starmer does decide to run against Streeting – and an alternative candidate from the left – the prime minister would have a major advantage because of Labour’s voting system, which is preferential.

MPs say they are deeply concerned that because Starmer would likely collect most second preferences, in a three-way contest he could even come second and still remain leader and prime minister.

There could also be a number of wildcard candidates from the cabinet and other MPs, including Lucy Powell, Bridget Phillipson, Yvette Cooper, and Al Carns.

With Burnham out of the race in the immediate future, his allies in parliament have begun casting around for alternative plans. “Stopping Wes is the top priority,” said one.

“MPs won’t take the chance that Starmer could win – the soft left will not allow that. There will be a candidate, the idea of Wes losing to Starmer is absolute madness,” another MP allied with Burnham said.

“Wes could end up like Owen Smith, that is absolutely the end of your political career,” one MP said.

While Streeting could gain support from some more resigning ministers on Thursday, some MPs were furious at what they saw as him destabilising the party when it was meant to be presenting its programme for government. “Colleagues are very, very, very angry with Wes,” said one MP supporting Starmer to stay on in the job.

Earlier on Wednesday, Zubir Ahmed, a close ally of Streeting who quit as a minister on Tuesday, renewed calls for the prime minister to resign, saying his authority had “irretrievably ebbed away”.