Keir Starmer is braced for Ed Miliband to resign next week as part of a co-ordinated coup to force him out.

Allies of the Prime Minister believe the Energy Secretary is poised to lead a wave of ministerial resignations if Sir Keir refuses to bow to Andy Burnham's demands to quit.

Home Secretary Shabana Mahmood has also been placed on resignation watch amid reports that she has done a deal with Mr Burnham – a claim she denies.

Allies of the PM insist he is serious about fighting for his job and has already drawn up a list of loyal MPs who could fill vacant posts.

A source told the Mail: 'Andy's level of entitlement is off the scale. He wants a coronation so he doesn't have to face any scrutiny and it seems he is willing to cause as much disruption to the Government as possible to get it.

'We are braced for some spectacular resignations next week. Ed thinks he's going to be Andy's chancellor and all the signs are there that he is getting ready to walk.

'Shabana has been having conversations with Andy's team – she could go too.

'All of it is designed to pile pressure on the PM to go quietly. If it works, then certain newspapers would be justified in describing it as a Left-wing coup.'

Voters go to the polls today in the crunch Makerfield by-election, which Mr Burnham hopes to use as a vehicle for his ambition to take the keys to No 10.

If he sees off the local challenge from Reform UK, he is expected to issue a private ultimatum to the PM this weekend, telling him he must set out a timetable for departure or face an imminent challenge.

Sir Keir on Wednesday insisted again that he will not step down.

In an apparent peace offering he suggested that Mr Burnham could be offered a 'big' role in the Cabinet.

But the PM insisted Mr Burnham should first keep his promise to lead the fight to retain Labour control in the by-election for the Greater Manchester mayoralty which he has triggered.

At the G7 summit in France the PM said: 'First and foremost, I want Andy Burnham to win, and that's why I've encouraged activists and members to go up there during the course of the campaign, and they'll be up there tomorrow helping to get the vote out.

'Then what happens is we're immediately tipped into a Manchester mayoral contest by-election, one of the biggest by-elections that we've ever fought, because of the scale of it.

'And it's really important to my mind that the whole of the Labour Party and Labour movement focuses on that, which is the next most immediate task.'

Sir Keir insisted he does not 'feel bitter' about the Labour leadership crisis and suggested he wants Mr Burnham to 'have a big role' in his Government, describing him as a 'huge asset'.

But on Wednesday allies of Mr Burnham said he will not take a job in Sir Keir's Cabinet if he is successful in Makerfield today.

A source on his campaign team told the Manchester Evening News: 'The benefit Andy has is the wind of change for not having been associated with the Government's failings.'

The source also warned No 10 against trying to 'put further challenges up' to Mr Burnham.

Sir Keir has spent weeks insisting that he will fight any leadership election, saying he will 'not walk away' from his election mandate.

Behind the scenes, he has also been putting together a campaign team, including sounding out potential donors and wargaming potential resignations by supporters of Mr Burnham and former health secretary Wes Streeting – who said on Wednesday he could mount a challenge as soon as next week.

Even at the G7 Summit he made time to take part in canvassing calls with Labour members back in the UK.

Labour sources predict Housing Secretary Steve Reed could serve as Sir Keir's campaign chairman and could even launch a fightback codenamed 'Operation Save Keir' as early as Friday morning in the immediate wake of the Makerfield result.

An ally of Sir Keir claimed he had made his mind up to fight on after a 'wobble' last month when he considered quitting.

'He does think he deserves to serve out his term. But there is also a public service aspect to it,' the source said.

'He strongly believes that handing the keys to someone who is largely unproven, with no scrutiny would be completely irresponsible.'

The prospect of a drawn-out Labour civil war is alarming other Cabinet ministers who fear party infighting of the kind that brought down the last Tory government.

One Cabinet minister told the Daily Mail: 'We have a responsibility to keep doing our jobs and keep the business of government going. The public will not forgive us if we descend into the chaos we saw under the Tories.'

Ms Mahmood is known to have warned Sir Keir privately last month that he should set out a timetable for his departure after the disastrous local elections in which Labour lost 1,500 council seats in England and trailed in third in Scotland and Wales.

But aides denied she is poised to resign to help force the PM out and was 'focused on her job'.

Mr Miliband did not respond to questions about whether he is planning to resign next week.

Once close, he and Sir Keir have fallen out in recent months. The Times reported he is refusing to take the PM's calls.

Downing Street denied the two men were not speaking.