Ed Miliband has come under fire from senior figures in his own party, as a poll showed the Tories moving into a two-point lead.
The Labour leader was accused by party grandee John Prescott of showing a severe lack of ambition in a damning assessment of his "far too timid" strategy and underwhelming conference performance.
Two prominent Labour donors joined the criticism. Lord Noon, one of the party's significant individual benefactors, was quoted by the Sunday Times as saying the party "really need to buck up" and dismissing plans for a mansion tax on £2 million-plus homes as "hopeless and desperate".
Lord Levy, who was Tony Blair's chief fundraiser, also criticised the tax proposal - part of a package to pay for extra NHS investment.
"I think that is a policy that is totally inappropriate and I see no validity in that policy whatsoever.
"Do I believe that the party needs to be more close and friendly to business? Yes, I do."
The YouGov survey for the Sunday Times suggested that Mr Cameron had scored a significant conference bounce as his party moved to 36%, with Labour on 34%, Ukip 13% and the Liberal Democrats 7%.
A week ago the Conservatives trailed by five.
Mr Miliband continues to lag badly behind the PM in personal ratings, with 22% saying he is performing well and 68% poorly, a net score of minus 46 points. By contrast Mr Cameron's ranking is only just negative - by 45% to 49%.
Mr Prescott said the Opposition leadership appeared to have resigned itself to not winning an overall majority at the 2015 general election and was seeking only to shore up its "core vote".
Urging Mr Miliband to "go all out for the win", he warned that "time is running out" to set out vote-winning policies to compete with the "belter" of a tax cut offer proposed by David Cameron at the Tory conference.
New Labour's 1997 landslide victory was secured by appealing to a broad range of voters across the country, the former deputy prime minister wrote in his Sunday Mirror column.
"But Ed seems to be pursuing a core vote strategy of getting 31% of traditional Labour supporters with a few ex-Lib Dem voters.
"He might as well have said at the end of his conference speech: 'Go back to your constituencies and prepare for coalition.'
"Ed might not like looking back but he can learn a lot from our 1997 campaign and our pledge card.
"Five polices on health, crime, jobs, education and tax that were costed, deliverable and drilled into voters on every doorstep. And at the next election we proved we delivered them.
"So come on Ed. Ditch the pollsters, the focus groups and US-style politics. Be bold, be brave and let's go all out for the win."
The "flat" Labour conference was a waste of a golden opportunity to enthuse voters, he wrote, while the Tory gathering the following week was marked by " smiles on faces, a confident leader and policies galore".
"Labour had a great opportunity to put flesh on the bone, with papers and TV channels giving Ed Miliband and his team a blank page to get their policies across. But bar a mansion tax to fund an increase in NHS funding and raising the minimum wage to £8 an hour by 2020, nothing sticks in my mind.
"I do remember Ed Balls saying he would freeze child benefit but I can't see many people racing to the polling booths for that. There was no mention of what we achieved in Government. I'm told that's because Labour is 'focused on the future not the past'...
"But the Tories are screwing us on our past so we can't have a future.
"Miliband's six-point 10-year plan was a start, but can you remember what they were? They were just one-line objectives, not detailed policies. I can understand keeping policies until the election begins but time is running out."
Pointedly contrasting Mr Cameron's speech "at a lectern" with the notes-free approach of Mr Miliband which led to him being mocked for forgetting to talk about the deficit, Lord Prescott said the Tory leader's tax cut promise was a con.
"But as election bribes go, it's a belter. The Tories may lose the next election but, by God, they're not going down without a fight."
He concluded: " Labour's approach is far too timid. I fear shadow cabinet ministers aren't delivering new policies because Ed Balls won't approve them if they involve spending commitments.
"That's because after the 2010 election, Labour allowed the Tories to start the false premise that we wrecked the economy and spent too much."
Shadow chancellor Ed Balls defended the leader's speech - insisting it scored "10 out of 10" despite the omission of the section about the deficit.
But he conceded that voters were "still getting to know" Mr Miliband with only eight months until the country goes to the polls.
"He has got to show himself and the policies of the next Labour government. He has got seven months to do that. When it comes to the TV debates he will be right up there head-to-head with David Cameron," he told the Murnaghan programme on Sky News.
"I think people know David Cameron, the Prime Minister, for all his faults. With Ed Miliband, people are still getting to know him. I think that by the time we are getting to general election day we are going to win that argument."
Responding to Lord Prescott, he said: "John Prescott is a fighter. Sometimes literally," he said in a reference to the punch thrown by the then cabinet minister during the 2001 general election campaign.
"But he is also a political fighter and we have a hell of a fight on our hands to save our National Health Service, to stop the 'strivers' tax' and to deliver our country from a Conservative Party that would take our country out of the European Union.
"John is clear in his article that we should learn from 1997 and I agree," he said.
"The lesson we learned in 1997, when John and I worked together, is if you as a party come along - which happened in previous elections for us before 97 - with promises which couldn't be paid for then you get into trouble.
"Everything in 97 was costed and paid for, everything in 2015 costed and paid for, no spending requiring more borrowing.
"The people who are making unfunded commitments are now the Tories and the Liberal Democrats."