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.