The Tories and Labour are polling less than 30% each for the first time in more than three decades, according to a new poll.
Lord Ashcroft poll put the Tories on 29%, one point ahead of Labour on 28%, the first time this has happened since 1981, according to analyst Mike Smithson. The previous Ashcroft poll last week put the Conservatives at 34%, while Labour's figure has remained stable.
Lord Ashcroft also showed the type of animal a focus group said each party leader would be.
They said Cameron would be a fox for "being smart and sleek" or a giraffe "looking down on everybody”.
Nigel Farage was "a peacock, or a weasel" while, most damagingly, Nick Clegg was dubbed “a Chihuahua in David Cameron’s handbag”.
Ed Miliband was described as “certainly not a predator… one of those animals that, when you go to the zoo, you’re not bothered whether you see it or not.”
Writing on his blog, Lord Ashcroft said the focus groups of undecided voters showed an "absence of any enthusiasm for Labour".
He wrote: "Perhaps the most notable feature of these groups of undecided voters was the absence of any enthusiasm for Labour – even among those who had voted for the party in 2010 – or any urgent desire for change.
Nobody could recall any Labour promises, and the most positive thing anyone said about Ed Miliband was that 'he talks sense on things like not privatising the NHS, but he’s not really on the ball, not in David Cameron’s league'.
"People could not say where he wanted to take Britain: 'He hasn’t really made up his mind where he’s going… it’s as though he just wants to be a politician, and he’s faffing around to find some principles' – and, ominously, 'it feels like he’s the interim Labour leader until the next one'."
Lord Ashcroft's poll showed Ukip on 15%, the Lib Dems on 9% and the SNP on 5%.
He noted that the Greens, polling at 11%, three points higher than his last poll, could be a cause for cutting the support for the two parties.
"One factor could be that the Greens have benefited from their prominence in the arguments over TV debates – in which case it will be interesting to see in the coming weeks whether they can sustain their share," he wrote.
The focus groups were aware of the controversy over which parties should be invited to the TV leaders' debate but they were not convinced the Greens should be included, as Cameron has insisted.
One woman described them as being "a bit more niche than Ukip".
Despite the huge volume of election coverage already in the press ahead of May's election, a total of 49% said they were paying little or no attention to it.