The Ipsos Mori poll puts the Tories on 35 per cent five points ahead of Labour on 30 per cent, while, in a further boost for the Tories, Ukip’s support appears to be on the wane down to 10 per cent and the Lib Dems are on eight per cent.
The survey comes after another Ipsos Mori poll in Scotland put the SNP on 54 per cent and Labour on just 20 per cent suggesting that the Nationalists will take all 59 of Scotland’s seat depriving Labour of 41 MPs.
With Mr Cameron needing to win by seven points to guarantee a majority the polls appear to suggest that the showdown on BBC Question Time may be a last chance for Labour leader Ed Miliband to turn the election around in Scotland and the rest of the UK.
The event hosted by David Dimbleby begins at 8pm on BBC1 with Mr Cameron first up for half an hour taking questions from an audience, followed by Mr Miliband and Lib Dem leader Nick Clegg.
A separate segment will then be played in Scotland from Edinburgh with BBC’s Glen Campbell hosting an audience with SNP First Minister Nicola Sturgeon while in England Ukip’s Nigel Farage will take questions.
An under-fire Mr Miliband, who was accused of complacency over Scotland, tried to rally supporters ahead of the debate stating that his party had hit its target of 4 million contacts with voters.
He announced that in the last week Labour would aim for another million contacts.
He claimed that Labour policies including £8 per hour minimum wage and an end to what Labour calls “exploitative” zero-hours contracts would provide a “bedrock of security for working families”.
He accused the Conservatives of “planning to devastate family finances” by cutting tax credits and child benefit in order to help make £12 billion of welfare cuts, an accusation dismissed by the Tories.
But Mr Miliband suffered a blow on the World at One when Labour former Home Secretary David Blunkett said that he is “unable to offer a majority Labour government because of what’s happened in just one part of the UK”
Mr Blunkett also warned Mr Miliband would have to do a deal with the SNP.
He said: “An incoming Labour government led by Ed Miliband will have to reach out across political divides”
Tory chairman Grant Shapps said: “This is the first crack in Labour’s dam. In a major intervention, a former Labour Home Secretary admits what all the polls show – it is impossible for Ed Miliband to get the keys to No10 without being propped up by Nicola Sturgeon and Alex Salmond.
“Next week, Ed Miliband could be Prime Minister with the SNP pulling his strings. Working people will pay the price. There’s only one way of stopping this – vote Conservative next Thursday.”