Labour's lead over the Conservatives has dropped to just one point, its lowest for a year, according to The Independent's latest "poll of polls".
It suggests that David Cameron has emerged from the party conference season in a stronger position than Ed Miliband, who has barely made any difference to Labour's ratings in his first year as party leader.
Labour's lead has dropped by two percentage points in the past month. Mr Miliband's party is now on 38 per cent, down one point, while the Tories are on 37 per cent, up one point, with the Liberal Democrats on 12 per cent, down one.
John Curtice, professor of politics at Strathclyde University, who compiled the figures, said: "Although Labour has recovered more quickly from its 2010 debacle than the Conservatives did after their heavy defeats in 1997 and 2001, its performance in this parliament to date is certainly not strong enough to suggest that it is well on course to win an overall majority at the next election."
He added: "It remains to be seen whether this dip proves to be anything more than a blip, but Labour must be somewhat concerned that its current (and recent) lead over the Conservatives is below what it was at the equivalent stage in three of the last four parliaments in which Labour was in opposition." Ominously for Mr Miliband, the improvement in his personal ratings during the phone-hacking controversy this summer has been lost, Professor Curtice said.
Mr Miliband has not yet convinced voters he is a potential Prime Minister, with his ratings in some polls echoing those of Neil Kinnock, the Labour leader who lost the 1987 and 1992 elections. "Mr Miliband's clear task by the time that the next party conference season comes around is to persuade people that he does have the ability to lead his country after all," said Professor Curtice.
His analysis of the regular polls taken by ComRes, ICM, Ipsos Mori and YouGov found that Labour would not secure an overall majority if the results were repeated at the next election. Proposed changes to constituency boundaries would make it even harder for Labour to win.
"Doubtless Nick Clegg and Mr Miliband will be more disappointed at their apparent lack of impact than Mr Cameron," Professor Curtice concluded. "Despite the tough public expenditure medicine and an ailing economy, the Tories are still holding on to most of the votes they won a year ago. Politically at least this age of austerity is looking very different from that with which Mrs Thatcher's regime had to deal in the early 1980s."
Labour is struggling to persuade people it is competent enough to do any better. "It still has to convince that it could provide the country with a viable alternative government," said Professor Curtice.
Yesterday the Tories seized on remarks by Charles Clarke, Labour's former Home Secretary, who told the BBC's Daily Politics programme that Labour had failed to come up with an alternative and that Mr Miliband had not succeeded in setting out a vision.
Baroness Warsi, the Tory chairman, said: "Ed Miliband is a weak, unconvincing and visionless leader. Charles Clarke is right; Labour offers no credible plan for the economy, just a plan B for bankruptcy."
Today Labour will hit back by staging a Commons debate on the economy and forcing a vote on its five-point plan to boost growth.