Alistair Darling castigated Labour for looking like it has lost "the will to live" and urged the party to mount a spirited fightback as the General Election approaches.
In a pre-conference interview, the Chancellor said: "We don't look as if we have got fire in our bellies. We have got to come out fighting."
But he acknowledged that he and Prime Minister Gordon Brown had their own roles to play in lifting Labour's morale.
"From the Prime Minister, the Chancellor, every Government minister. It is all our responsibilities," he told The Observer.
Mr Darling is one of several Cabinet ministers who have sought to rally the party ahead of its last annual conference before the next election.
Lord Mandelson, the Business Secretary, insisted that Labour should not be written off.
He told the Sunday Mirror: "This election is not in the bag - neither for us, nor the Tories.
"Every day we face in one way or another attempts to write Labour off or pretend that some of us are preparing for defeat.
"That's not my belief."
He insisted that the election was "up for grabs", rejecting suggestions that the poll was already decided.
Mr Darling likened Labour to a football team, saying: "Sometimes you see their heads go down and they start making mistakes and they lose the will to live."
Asked whether it was the "captain's job" to inspire the team, he added: "It is the responsibility of all of us, no matter where we are playing in the team."
But he offered his backing to Mr Brown. "Gordon is our leader. Gordon is the Prime Minister. Let's get on with the job in hand and fight for what we believe in."Reuse content