But Mr Starmer insisted he will not “walk away” from Downing Street, setting Labour up for a showdown over the premiership as the outgoing Greater Manchester Mayor insisted his win was “the change moment” for Britain.

Speaking to reporters at an event in north London, Mr Starmer said: “If there is a contest, then yes, I will stand.

“I have said repeatedly, I am not going to walk away from that.” 

The primer minister said he had not yet directly spoken with Mr Burnham since his victory, but added that he will, and had already sent a message of congratulations to him.

Mr Starmer also said his rival’s by-election victory was evidence “the tide is turning on Reform, that they can’t now win by-elections”.

At a Labour rally following his win, the leadership hopeful said: “We’ve been on a path for 40 years that simply hasn’t worked for people and places in this part of the world, and this now is the change moment.

“We have an opportunity to turn the tide, to make the country feel like it’s working again, to make people see that politics can make a positive difference, to make people feel hope again.” 

He added: “I think we need in this country right now for people to feel a sense of hope that there is something better to work towards on the horizon.” 

He called for reindustrialisation, reforms to Whitehall and an end to the “unfairness” of the immigration system, which he said people had raised frequently on doorsteps during his campaign.

Makerfield is the third successive parliamentary by-election in which Nigel Farage’s political outfit has come second over the last year, following the Caerphilly by-election for the Welsh Parliament in October, and the Gorton and Denton Westminster by-election in February.

Mr Burnham defeated Reform UK’s Robert Kenyon by 9,231 votes, up from 5,399 in 2024, and Labour’s vote share increased by 9.61%.

In his victory speech after winning the Makerfield by-election, Mr Burnham said Labour had a “final chance to change”, and he urged his party to act now, saying there would be no second chance.

He said: “Everyone knows that politics isn’t working.

“Everyone can feel that the country isn’t where it should be. Tonight could, just could, be the turning point.” 

In a direct message to Labour MPs he said: “I do say to my own party: this is a final chance to change.

“This is what people said directly to me on the hundreds of doorsteps that I stood on.

“We must hear it, we must act upon it and we must get it right. There will be no second chance.” 

Mr Burnham gave up the Greater Manchester mayoralty by becoming Makerfield MP, winning the seat that was vacated by Josh Simons in order to allow him the chance of returning to Westminster and seek to become prime minister.

In an attempt at addressing the assertion that he was only seeking to become Makerfield’s MP to further his own ambitions, he said: “It will never be a stepping stone to me, but instead will be my touchstone.

“A Makerfield test at the heart of British politics will make sure that the places Westminster has neglected will now get fairness.”