Former minister Stephen Byers has called on fellow supporters of Tony Blair to unite behind new Labour leader Gordon Brown.
Mr Byers was one of Mr Blair's strongest backers during the latter's ten years in No 10 but he has now called on diehard Blairites within the Labour party to support Mr Brown's "left-leaning" agenda.
After a positive start to Mr Brown's premiership polls have shown a large swing in support towards David Cameron's Conservatives, raising the possibility of defeat for Labour in next year's local elections.
Writing in the Observer newspaper, Mr Byers makes clear his commitment to unity within the Labour ranks driven by the prospect of a "tough year" for his party.
"With Tony Blair gone from domestic politics, the task of leading Labour to victory falls to Gordon Brown. It is the responsibility of all of us who want to see a fourth election victory to give him our support," he writes.
"Tony Blair is history. He is the political past and will not be part of the future of domestic politics in our country."
Mr Byers made clear his belief that the election will only be won with a broad range of policies attracting the middle ground, saying "motivating the core. will not be enough".
"We also have to appeal to the promiscuous voter by demonstrating that we can be the party of aspiration and ambition as well as social justice and fairness," he added.
Senior Cabinet minister Jack Straw has said his party has been struggling against the Conservatives in an unusually frank admission.
The justice secretary told today's Times newspaper he believed Mr Cameron's policies were "resonating" with the public.
"Politics is about change and governments, if they want to stay in government, have to adapt with changing circumstances," he said.
"We have to show the people we are making decisions that are relevant to their futures and not just resting on our laurels."