British Prime Minister Keir Starmer said Friday he would not step aside, vowing to resist any challenge from Labour leadership rival Andy Burnham, a move that could deepen political instability.

Burnham, the mayor of Greater Manchester, secured a decisive victory in Makerfield in northwest England to enter Parliament and has indicated he would be prepared to contest any leadership race to replace Starmer.

His win has intensified pressure within Labour, with a growing number of lawmakers urging Starmer to consider stepping down amid declining popularity and rising support for the populist Reform UK Party in opinion polls, arguing it could allow for a smoother transition to Burnham.

If that scenario unfolds, Britain would be on course to install its seventh prime minister in just over a decade, the highest turnover in nearly two centuries, underscoring public frustration over stagnant living standards, strained public services and persistent concerns over illegal immigration.

But Starmer, who led a landslide election victory in 2024, said he is "not going to walk away,” reeling off a list of priorities: closer ties to the European Union, stabilizing the economy and reducing waiting times in the health service.

Burnham hits national themes in speech

"If there is a contest ... I will stand, and I’ve said repeatedly I’m not going to walk away,” Starmer told reporters in London.

In a call with Labour staff across the country, he warned of the dangers of a potentially disruptive leadership campaign, urging them instead to focus on retaining the mayoralty of Greater Manchester.

"The one thing we’ve got to avoid doing is plunging our party and our country into chaos by turning on each other and tearing apart our party,” he said. "That has never worked.”

His resistance to growing Labour calls to step down could mean the party airs its divisions in public in a leadership contest, something that undermined the Conservatives, who lost power after changing leaders five times in eight years.

Burnham, a 56-year-old career politician, took 54.8% of the vote to the populist Reform UK candidate’s 34.5%, boosting his image as someone who could halt the rapid rise of veteran Brexit campaigner Nigel Farage’s party.

Hours after claiming victory, he set out a national approach in what lawmakers called a prime ministerial-style address.

"I did talk about the need to change Labour ... and we’ve got to now take this moment and answer the challenges that have been laid down,” he told a crowd of supporters, listing priorities including making life more affordable, reducing utility bills and driving reindustrialization.

"It is our last chance to change, but we are going to take it ... and we are going to lay out a new path for Britain.”

His victory not only sent him back to Parliament, from where he can mount a leadership challenge, but also boosted the hopes of some worried Labour lawmakers that they can win the next national election, due in 2029.

Many believe Starmer, who has some of the weakest popularity ratings of any British leader, cannot achieve that.

Burnham broadly popular among Labour members

Polls of Labour Party members indicate Burnham would win a formal leadership contest, although some Labour lawmakers hope such a contest can be avoided.

Starmer, 63, has repeatedly vowed to fight on despite scandals, policy U-turns and accusations of indecision, aiming to complete his five-year term by delivering on his pledge to address Britain’s most pressing problems.

About a quarter of his lawmakers have urged him to quit since Labour suffered heavy losses in local elections last month, and more have added their names. Senior colleagues, including the defense and health ministers, have resigned.

Some Labour lawmakers said the party should give Starmer the weekend to reflect and consider stepping down. A Burnham ally, Labour lawmaker Louise Haigh, told the BBC she hoped "that Andy and the prime minister can speak over the coming days.”

"We want to avoid a leadership contest if possible, and we hope that we can agree on a way forward,” she said.

Many Labour members of Parliament fear losing their seats in the next election, due in 2029, to Farage’s party, which has led opinion polls for more than a year.

Another of Starmer’s rivals, former health minister Wes Streeting, said this week he would force a contest soon unless the prime minister announced when he would step down. He said Burnham’s victory was proof Labour needed change.

Party rules require 20% of the parliamentary party, or 81 lawmakers, to back a single candidate to trigger a leadership challenge.