Wes Streeting has confirmed he will be standing, should a Labour leadership contest to replace Labour Party leader and British Prime Minister Keir Starmer be triggered.
"We need a proper contest with the best candidates on the field, and I'll be standing," he told reporters at a conference in central London.
Mr Streeting, who this week stood down as health secretary, also insisted he did have enough support among MPs to trigger a contest, but suggested his challenge would "lack legitimacy" without rival Andy Burnham being given a chance to return to Parliament.
He told the Progress think tank conference: "Firstly, I do have support in the parliamentary party, but this week I also had a choice.
"We could have rushed straight into a leadership contest, knowing not all of the candidates would be on the pitch, that Andy Burnham was about to stand in a by-election, and that if we had rushed ahead without giving Andy a chance to stand, the new leader, whether it was me or anyone else, would lack the legitimacy, and so we would end up extending instability and uncertainty.
"That might have been the self-interested thing to do for candidates who are in Parliament presently, but it wasn't in the party's interest and wasn't in the national interest."
Mr Streeting is among the senior Labour figures to call for a debate over the future of the party's soul, amid the crisis that has engulfed it after a bruising set of election results across England, Scotland and Wales.
Burnham prepared to 'fight to the highest level'
Mr Burnham was cleared to run for selection in the Makerfield by-election.
He has said he is prepared to "fight to the highest level", as he and other senior Labour figures jostle to lead the party in the future.
Mr Streeting hit out at what he called an "overcautiousness" in Labour, which began when the party was in opposition and was carried over into Government.
"Instead of a willingness to challenge ideas and kick the tyres, debate was viewed as division and shut down," he said.
The Ilford North MP added: "That's why we need a proper contest where all candidates can put their best foot forward.
"It's got to be a battle of ideas so that whoever wins comes out stronger for it."
Elsewhere in his speech, Mr Streeting put forward what appeared to be a sketch of his own proposals for the Labour leadership.
Moving closer to Europe was the first of three major policy ideas Mr Streeting floated, and he told the conference: "We need a new special relationship with the EU, because Britain's future lies with Europe - and one day back in the European Union."
Mr Streeting also called for a debate over "what type of capitalism [do] we want" and how the UK creates and benefits from economic growth.
Thirdly, he insisted Britain must not treat "the destruction of shared truth" as inevitable, and said the country needed to look to the creation of the BBC amid the media innovations of the early 20th century as a blueprint for how to "take the pen back" from social media bosses in Silicon Valley.
Mr Streeting was among those who have backed Mr Burnham's bid to fight the impending by-election, which was triggered when Josh Simons announced he would down as an MP to give Mr Burnham a chance to return to Parliament.
'Big change moment is needed'
Mr Burnham told Channel 4 News this morning he was focused on winning a seat in Parliament, rather than ousting Mr Starmer as Prime Minister.
"It's just not the issue. The issue is winning. Winning a by-election with what I'm saying, you know, it's not about, you know, necessarily the next thing," he said.
But Mr Burnham said he had "made a whole career fighting for people in this part of the world", later adding: "I've taken that fight to another level as mayor and yes, I will carry on taking that fight to the highest level."
A "big change moment is needed" in British politics, he also said, following a bruising set of elections for Labour in England, Scotland, and Wales.
Applications for Labour's Makerfield candidacy close on Monday and the NEC will endorse a candidate on Thursday.
18 June is thought to be the earliest date a by-election could take place.
If he is successfully elected, Mr Burnham is widely expected to challenge Mr Starmer for the party leadership.
While Makerfield is typically a safe seat for Labour, the party expects a stiff challenge from Reform UK this time around.
Mr Simons secured a majority of just 5,399 over Nigel Farage's party at the 2024 general election.
Since then, Labour's polling collapse and Reform's surge have seen their positions reverse.
But Mr Burnham could benefit from his strong personal following across the north west, where he enjoys a net favorability rating of 24% according to pollster Ipsos, considerably higher than any of the party leaders or the Labour Party itself.
Candidate selection processes are already under way for Reform UK and the Greens.
