LONDON — Defence Secretary John Healey has told his party’s warring leadership rivals that the “very credibility of Labour in government is at stake,” as the contenders to replace Keir Starmer as prime minister set out their stalls.

In a speech in central London on Tuesday evening, Healey said: “We must get serious. It’s not about us, not about the insiders of politics, it’s about the interests of this country.”

“We must be a government that steers Britain through the conflicts we’re in and the crises we face,” he told an event organized by the Good Growth Foundation.

Keir Starmer’s leadership has been dealt a severe blow over the past fortnight as almost 100 MPs said that he should set out his timetable to step down as prime minister. Several of his ministers, including Health Secretary Wes Streeting, have resigned to trigger a contest to replace him.

Earlier on Tuesday, Andy Burnham, the mayor of Greater Manchester, was selected as Labour’s candidate for the Makerfield by-election. He has been talked up by several Labour MPs as a potential successor to Starmer and as one of the few politicians in their party viewed positively by the electorate.

Reform UK, which is leading the polls in Britain, has pledged to “throw absolutely everything” at the by-election.

POLITICO has also reported that Healey’s junior defense minister, Al Carns, is being urged by MPs to consider a leadership bid. Two government officials suggested that he should not have written a frank post-mortem of Labour’s local election loss for the New Statesman last week.

Healey told the event that it has been a “difficult few weeks” and that “For Labour, the last 10 days has been tough,” as he warned that his colleagues have “turned in on ourselves.”

In a warning to those seeking to unseat Starmer, he said that he has “not forgotten the pains” of being in opposition, adding: “We must not throw away so lightly the power we were given.”

In what appeared to be a swipe against Burnham — pictured by photographers out jogging — he said: “I don’t care about photo opportunities or PR firms. Politics — to me — is not about the individual.”

“People will not forgive us if they think we’re more concerned about ourselves than we are about them,” Healey said.

The Cabinet minister used his speech to announce investment in 13 of “Britain’s next Defense Unicorns.” Britain’s defense industry is awaiting the publication of Labour’s delayed Defence Investment Plan (DIP), which will lay out how the government will invest in and grow the country’s defense capability.