Angela Rayner has officially launched her bid to become the deputy Labour leader, with a warning party faces the “biggest challenge in our history”.
The shadow education secretary had previously been seen as a likely candidate to succeed Jeremy Corbyn as leader.
But instead she has thrown her support behind her friend and flatmate Rebecca Long Bailey.
Speaking in Stockport on Monday, Rayner said Labour faces the “the fight of our lives” following its general election defeat.
“The quick fix of a new leader will not be enough. We must rethink and renew our purpose and how we convince the people to share it,” she said.
“Either we face up to these new times or we become irrelevant. The next five years will be the fight of our lives and I’m standing here today because I don’t run away from a fight.
“It is why I want the leadership of our party to be a team effort. I will be quite straightforward: I will be voting for my friend Rebecca Long Bailey if she stands for the leadership.”
Rayner added: “As a Party we face a choice: win or die.”
The MP for Ashton-under-Lyne also hit back at claims she and Long Bailey represent “continuity Corbyn”.
“As a northern working class lass I’ve been underestimated and told my place ever since I was born,” she told Sky News. “Two northern women will not be told they are continuity anything from any man.”
Tom Watson, the former deputy party leader who stepped down from parliament at the election, this morning said Long Bailey was the “continuity candidate” who “stands for Corbynism in its purest sense”.
Richard Burgon, the shadow justice secretary, has already announced his intention to stand for the deputy job.
Labour’s ruling National Executive Committee (NEC) will later today decide on the campaign timetable and other key elements for the leadership election.
The meeting will consider factors that could potentially affect the outcome, such as the “freeze date” for eligibility to vote for those signing up and the cost of becoming a registered supporter – non-party members who can vote in the race.
It comes as Corbyn’s allies are facing a backlash over plans to radically reshape the party before he steps down this spring.
Multiple sources have told HuffPost UK that party general secretary Jennie Formby and Corbyn’s chief of staff Karie Murphy are drafting proposals to “embed Corbynism” with a major staffing reorganisation expected to start this week and end in March.
Keir Starmer, the shadow Brexit secretary, has emerged as the early frontrunner in the race to succeed Corbyn.
Long-Bailey, the shadow business secretary and favourite of the current leadership, is expected to formally declare her candidacy soon.
Labour MPs Emily Thornberry, Jess Phillips, Lisa Nandy and Clive Lewis are also standing.