Starmer says he will stand in any Labour leadership contest against Burnham | Keir Starmer

Keir Starmer has said he will stand in a Labour leadership contest should one be triggered after Andy Burnham’s decisive victory in the Makerfield byelection, adding he will not “walk away”.

He also warned that such a contest would “plunge us into chaos” and that Labour needed to “pull together” to contest the byelection to replace Burnham as the mayor of Greater Manchester.

The prime minister told reporters at an event in north London: “If there is a contest, just to be clear with you, then, yes, I will run.”

Despite Starmer’s insistence he will fight any challenges, the scale of Burnham’s victory in the Makerfield byelection, with 55% of the vote, has prompted further calls for the prime minister to consider his position.

In his victory speech, Burnham said the result “could be a turning point” and that people had “voted for change. They have voted for more power for the north and everywhere forgotten by Westminster.”

At a later rally, he in effect set out a programme for government and said “the word Makerfield in the future must be known as a byword for the change that came to British politics”.

“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 said.

Louise Haigh, the former transport secretary who helped lead Burnham’s campaign, called for Starmer to avoid what would be a “brutal and unpleasant” leadership contest and set out a timetable for his exit.

Speaking after Burnham’s victory rally, she said there was a plan “ready to go” if Starmer refused in the coming days to step down.

She added: “I hope the prime minister takes the weekend to really reflect on the result here, listen to soundings from the cabinet and from the PLP [parliamentary Labour party] because all the evidence suggests that contest would be brutal and unpleasant and it would be very unlikely that the prime minister would win at the end of it.”

Patrick Hurley, the Labour MP for Southport, told the Guardian he took “no pleasure” in calling for the departure of Starmer, whom he praised as a “monumental figure” for winning the 2024 election.

But it was time for new leadership, he said: “We’d almost forgotten what it felt like to have hope and optimism to win an election – that’s been in short supply over the last 18 months.”

Some Burnham supporters had hoped the prime minister might decide against contesting a leadership race, with allies of the outgoing mayor saying he wanted to come to an agreement with Starmer next week about a timetable for a handover of power.

However, Starmer’s indication that he will not allow a coronation for Burnham could set up a more protracted contest, with other candidates potentially coming forward as well. As the sitting Labour leader, Starmer will automatically be on the ballot if he decides to take part.

The prime minister was understood to have spoken to cabinet allies on Friday morning, as he sought to shore up his position. He also spoke to Labour staff across the country, saying it was time to “pull together as a party” and avoid “turning on each other and tearing apart our party and our movement”.

In a challenge to Burnham’s ambitions to replace him, Starmer stressed his “mandate two years ago” from the July 2024 general election in which he was elected with a landslide majority.

“In relation to what happens next, obviously, we had a mandate two years ago to carry out change and we’ve done incredible things … There’s more to do and that’s what I’m focused on. It is what I was elected to do, which is to serve my country.”

Starmer’s strategy is to put as many obstacles as possible in the way of Burnham, including the suggestion that the Greater Manchester mayoral election to replace him should take place first.

However, the bigger than expected majority in Makerfield against Reform UK heaps more pressure on the prime minister to consider standing aside. Starmer has already indicated he could offer his rival a top job, which Burnham has rebuffed. He said on Friday morning that he had not spoken to Burnham yet but that he would and had sent his congratulations.

Starmer framed the win in Makerfield as a sign Labour was making gains against Reform, rather than it being a personal victory for Burnham.

“I think it’s further evidence, actually, if you look at it in the context of other byelections, that the tide is turning on Reform, that they can’t now win byelections,” he said.

“They’ve reached probably the peak of their support; it is going down. So, very good, congratulations to Andy Burnham, but actually the tide is turning on Reform as well, so this is really important in that respect.”

One idea put forward by Harriet Harman, the former deputy leader of the party and now Starmer’s adviser on women and girls, is for Labour MPs to oversee a contest rather than the decision being put to the whole party membership.

She suggested Labour MPs should be given a vote on “who they want as prime minister”, telling BBC Radio 4’s Today programme: “The way you get to be prime minister and the way you govern the country is by having the support of the majority of the party in parliament.

“So, whoever’s prime minister has to have the support of Labour MPs, and I think what should happen is that the three contenders – which is obviously Keir Starmer, who’s the prime minister; Andy Burnham, who’s the challenger; and Wes Streeting, who’s also a challenger – should be got in a room by the deputy leader of the Labour party, Lucy Powell, and the chair of the parliamentary Labour party, Jess Morden, to agree a process whereby the Labour MPs choose who they want.”

She added: “There must be a woman in the contest” as “we cannot have a male beauty parade again”.