Andy Burnham has secured his return to the House of Commons as his allies called on Sir Keir Starmer to hand over power.
The Greater Manchester mayor won the Makerfield by-election by 9,231 votes, seeing off the challenge from Nigel Farage’s Reform UK.
Mr Burnham’s victory sets up a potential leadership contest unless the Prime Minister agrees to step down.
In his victory speech he said Labour had a “final chance to change” and “we must act upon it”.
Sir Keir has insisted he will fight any attempt to challenge him and has been building up a war chest for a leadership campaign.
But Mr Burnham’s supporters urged the Prime Minister to set out an “orderly and managed transition” of power.
Former cabinet minister Louise Haigh said she hoped Sir Keir will “do what’s best for both the country and the Labour Party”.
Mr Burnham increased Labour’s majority in a seat which voted for Reform in council elections last month.
Following his decisive victory 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.”
He added: “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.”
