Zack Polanski is facing mounting pressure from within the Green Party to do a deal with Labour that would help Andy Burnham beat Reform UK in the Makerfield by-election.

Party politicians and activists including a former leader have told Mr Polanski that it is in the party’s interests to lend support to the Greater Manchester mayor on June 18.

The first poll of the campaign at the weekend suggests that Mr Burnham has just a three-point lead over Reform’s Robert Kenyon, while the Greens are down in fifth with no chance of winning. 

The Greens, who will tonight choose a new Makerfield candidate after their original one quit, are divided over how hard to fight the campaign, with hardliners saying they should take on Labour as well as Reform.

But the activists, who have signed a joint statement, argue that if Mr Burnham wins and goes on to become prime minister he would bring in electoral reform in the shape of proportional representation.

The Greens won four seats in the 2024 general election, but analysis suggests that if proportional representation had been used instead of the traditional ‘first past the post’ system, they would have won 71.

The group, which includes Jonathan Bartley, a London councillor and co-leader of the party from 2016 to 2021 warned the contest must be approached with ‘trepidation’ – as Mr Burnham‘s appointment could offer a ‘unique opportunity’ to reform the voting system’.

‘If Burnham will commit to backing proportional representation for the next general election Labour manifesto so that it is in place by the election after next, then on this unique occasion we don’t think Greens should run a full campaign against him,’ the statement said.

But a Green Party spokesman told The Times: ‘We respect all views from within the party on this issue. As a democratic party this is a decision for local members and a democratic candidate selection process is currently underway.

‘We are not aware that Andy Burnham is ready to make, or indeed has the authority to make, any kind of deal. The people of Makerfield deserve to have a choice about who they feel best represents their interests.’

It adds further weight to calls for Right-wing parties to unite to defeat Mr Burnham, with the Survation poll showing Reform could win with the backing of other parties.

Senior Greens have signed a join statement saying Zack Polanski should consider giving Labour a clear run in the Makerfield by-election

The Green letter was signed by former party leader Jonathan Bartley, above, and ex-councillor and author Rupert Read

The first poll of the contest put Labour on 43 per cent support, with Reform on 40 per cent as Andy Burnham bids to return to the Commons

The letter admits Makerfield is ‘not a seat the Greens can win’ – adding ‘it will be a straight fight between Labour and Reform’, The Times reported.

A proportional representation voting system would allow for a closer reflection of smaller parties’ votes in Parliament.

Last week Mr Burnham said the current first-past-the-post system should change to enable ‘less point-scoring, more problem-solving’ and make politics ‘more place first rather than party first’.

Former Reform MP Rupert Lowe’s party Restore Britain was predicted in last week’s Survation survey to win 7 per cent of the vote – while the Conservatives were on 2 per cent.

Meanwhile the Lib Dems have been placed at 4 per cent and the Greens at 3 per cent.

Reform leader Nigel Farage said the findings exposed a two-way battle between Mr Burnham and Mr Kenyon in the Brexit-backing seat. 

‘Robert Kenyon is the only candidate who can stop Andy Burnham. This is a two-horse race – nobody else comes close,’ he said.

Nigel Farage said the contest was a ‘two-horse race’ between Reform candidate Robert Kenyon, left, and the Greater Manchester mayor

While Mr Lowe last week trumpeted an endorsement from Elon Musk, Conservative leader Kemi Badenoch has ruled out ‘any deals’ with Reform.

The parties were ramping up their efforts over the weekend, with less than a month until the vote on June 18.

The Greens previously ran into issues with their candidate Chris Kennedy who quit after 12 hours for ‘personal and family reasons’.

It followed the revelation Mr Kennedy had circulated an Instagram video referring to the arrests of two men over arson attacks on Jewish ambulances as ‘total bulls*** to keep the false flag flying’.

The tightness of the Survation poll numbers reflects a big personal bounce for Mr Burnham. Without him as the candidate Labour was seen as losing to Reform by an 11 point margin.

Over the weekend, former Conservative cabinet minister Jacob Rees-Mogg told the Daily Mail the message from the figures was ‘if you want Andy Burnham to be Prime Minister, vote Restore’.

‘It looks as if Conservative voters have decided to vote tactically,’ Sir Jacob said.

‘They clearly think that avoiding hard-Left Burnham – or flip-flop Burnham, whichever you prefer – is more important than their historic loyalties. And Restore voters don’t.

‘Voting for Restore is a waste and it’s bad for the country.’

On Friday Mr Burnham painted his bid to return to the House of Commons as an opportunity to get rid of Keir Starmer.

He said victory would mean ‘changing Labour’, with the widespread expectation he would mount a quick challenge for the keys to No10.

But Mr Burnham has been coming under increasing scrutiny over what direction he would take the Government.

He has already backed off from his pledge to rejoin the EU – a view popular among MPs but regarded as deeply unhelpful in an area that heavily endorsed Brexit.

Mr Burnham was believed to have told Home Secretary Shabana Mahmood he supports her tough immigration crackdown.

However, he has now wavered on whether changes to indefinite leave to remain should be retrospective – regarded as crucial for addressing the wave of arrivals from recent years.

Critics have also accused Mr Burnham of watering down his commitment to a proportional representation voting system.