The Greens are going to campaign for the Makerfield byelection, complicating Andy Burnham’s potential route back to parliament against what is expected to be a strong Reform UK challenge.

A statement from the Greens said candidate selection was in process and that the party had learned from its win in another Greater Manchester seat in February, when it overcame a 13,000 Labour majority in Gorton and Denton.

However, Caroline Lucas, the party’s former leader, said she disagreed with this course of action, writing on X: “I hope this isn’t true. There are times when it’s more important to put country before party. This is one of them. Burnham’s longstanding commitment to a fairer voting system could transform our democracy & counter dire threat of a Reform UK government.”

Labour has a smaller majority of just over 5,000 in Makerfield, where Reform came second in the 2024 election. The sitting MP, Josh Simons, announced on Thursday that he would stand down, saying he wanted Burnham, the Greater Manchester mayor, to replace him.

Burnham has said he will seek the Labour nomination, and while the decision is for the party’s national executive committee (NEC), which blocked him from fighting Gorton and Denton, Downing Street has indicated it will allow him to contest Makerfield.

With Reform having won all nine seats being contested for the constituency on Wigan council in local elections last week, Burnham is gambling that his personal appeal will counteract Labour’s poor national poll ratings and take him to a win.

There had been speculation that the Greens might not field a candidate in Makerfield or barely contest it, to avoid splitting the leftwing vote and letting Reform in. One possible mooted deal would have been for the Greens to stand down if Burnham agreed to look at electoral reform if he became prime minister, something he has already indicated he might do.

But in a statement on Friday morning, a Green spokesperson said: “We are looking forward to the campaign. We’ve learned from our campaigning and wins in Gorton and Denton and the recent local elections, and we’ve shown we can beat Reform. We’re a democratic party and our local members choose their candidates. We have already started the candidate selection process for any potential byelection in Makerfield.”

The Greens are highly decentralised, meaning that even if the leadership wanted them to stand aside, it would be up to the local party.

One Green source in Greater Manchester said that while the local party would have to make its own decision, much would depend on whether the weight of the national organisation was put behind the campaign. “With Gorton and Denton we showed that the national party operation focusing on an area can make a pretty monumental difference,” they said.

In 2024 the Greens came fifth behind Labour, Reform, the Conservatives and the Liberal Democrats in the constituency. However, the party has since surged in the polls under Zack Polanski, and in Gorton and Denton it was able to mobilise huge numbers of volunteers to canvass and campaign.

Burnham confirmed on Friday that he would ask the NEC to allow him to stand in the contest. This would require a byelection for his mayoralty, with concerns that Reform could win that.

Burnham said much bigger change was needed at a national level, singling out the cost of living crisis as a priority for his campaign, in a statement that set out why he wanted to return to Westminster.

“This is why I now seek people’s support to return to parliament: to bring the change we have brought to Greater Manchester to the whole of the UK and make politics work properly for people,” he said.