Liz Kendall has ruled out standing aside in the Labour leadership contest to help block the growing challenge from hard left candidate Jeremy Corbyn.
The shadow care minister insisted she will fight to the very end and warned that a victory by the veteran backbencher would be a "disaster" for the party.
Ms Kendall is reported to be under pressure to quit the contest to allow the moderate vote to rally behind one of her two centrist rivals – Andy Burnham and Yvette Cooper.
Asked if she would step aside, Ms Kendall told BBC News: "No. You never stop fighting for what you believe in. I will be fighting for what I believe in till the very end."
She added: "It would be a disaster. Turning back to the politics of the 1980s, which saw us suffer defeat after defeat does nothing to help the people we all came into politics to serve."
Ms Kendall has ruled out serving in a Corbyn shadow cabinet but insisted she would not leave the party if he wins in September.
"I'll never ever do that," she said. "That would be like me leaving my family."