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Newly elected Makerfield MP Andy Burnham addresses members and supporters of the Labour Party after he won the by-election, in Ashton-in-Makerfield, Britain, Friday.Temilade Adelaja/Reuters

Britain is facing weeks of political uncertainty as a leadership battle takes shape pitting Prime Minister Keir Starmer against Greater Manchester Mayor Andy Burnham.

Mr. Burnham’s by-election win on Thursday in a Manchester-area constituency has made him a frontrunner to challenge Mr. Starmer who is under increasing pressure from Labour MPs to resign.

He took 55 per cent of the vote in the Makerfield riding, finishing far ahead of Reform UK candidate John Kenyon. Most observers expected a much closer race and predicted Reform could even win the riding given the party’s large lead over Labour in most national opinion polls. In the end, Mr. Burnham won by more than 9,000 votes, or 20 percentage points.

Mr. Burnham needs to be an MP to take on Mr. Starmer, and he has made no secret of his desire to become party leader and prime minister

“We will take the energy of this campaign and we will bring it forward into changing British politics for the better,” Mr. Burnham told a rally of supporters on Friday. “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.”

Starmer said Friday he would stand in any leadership contest.

Reuters

Mr. Starmer offered his congratulations but insisted that he will not quit. “If there is a contest, then yes, I will stand,” he told reporters on Friday. “I have said repeatedly, I am not going to walk away from that.”

His reticence means Labour could be embroiled in a lengthy internal struggle.

“Britain is now on its sixth prime minister since 2016 and that instability looks likely to be further underlined by Burnham winning the Makerfield by-election,” said Tony Travers, associate dean of the school of public policy at the London School of Economics.

Mr. Burnham, 56, was first elected mayor in 2017 and he has won plaudits for reforming local transit. He was re-elected in 2021 with an even larger margin.

But he has drawn criticism for lacking a clear vision and flip flopping on issues. On Friday he highlighted the unfairness of Britain’s immigration system, promised changes to education and vowed to address the cost of living. He has offered few details.

Supporters say he is a strong communicator and the scale of his win over Reform demonstrates that he is best positioned to lead Labour to victory in the next election.

Reuters

Mr. Burnham’s win in Makerfield “is a remarkable result,” said John Sinclair who was an adviser to former Labour Prime Minister Gordon Brown. “For him to win more than 50 per cent of the vote in this current climate is huge.”

Mr. Sinclair added that the result also showed that “there is a desire to vote Labour if Labour can get the message right, and he did. And I think that makes Keir Starmer’s position entirely untenable.”

Mr. Starmer has struggled ever since guiding Labour to a massive victory in the general election less than two years ago. His government has done little to stimulate economy and Labour’s popularity has plummeted. The party suffered its worst showing ever in local election in May. Since then nearly 100 Labour MPs, roughly one quarter of the caucus, have called on him to resign and several high-profile cabinet ministers have quit.

Labour MP Dawn Butler said there was no longer any point in pretending that Mr. Starmer can remain as leader. “We had a really devastating set of local elections and people have told us what they want and they want to see a Labour government but they want to see a change of direction and that change of direction isn’t currently coming from our current Prime Minister,” she told Sky News on Friday.

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Labour party's Andy Burnham stands beside candidate Count Binface, left, and a candidate for Protect British Wildlife after winning the Makerfield by-election.Jon Super/The Associated Press

A leadership contest can be triggered if 20 per cent of Labour MPs, which currently would be 81, put forward a candidate. As the incumbent, Mr. Starmer would not have to be nominated. Party members and affiliated unions would vote to decide the winner.

Mr. Burnham is expected to easily meet the nomination threshold. Former health secretary Wes Streeting has also indicated he will have the backing of 81 MPs and is considering launching a challenge as early as next week.

The Manchester Mayor is no stranger to Parliament. He served as an MP from 2001 to 2017 and held several cabinet posts. He has also run for the party leadership twice, finishing fourth in 2010 and second to Jeremy Corbyn in 2015.

John Curtice, professor of politics at the University of Strathclyde, cautioned that Mr. Burnham’s win on Thursday doesn’t necessarily translate into national support. “Because if indeed he does become prime minister he will no longer be the challenger, he will be the incumbent, he will have to be defending his record,” Prof. Curtice told BBC.

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