The Conservative Party has opened up a five-point lead as Labour's core supporters desert the party, according to the latest monthly poll for The Independent.
CommunicateResearch found there has been a sharp rise in support for the Liberal Democrats, mainly at Labour's expense. The Tories are on 34 per cent (down two points on last month), Labour on 29 per cent (down eight points), the Liberal Democrats on 21 per cent (up seven points) and other parties on 16 per cent (up three points).
To help determine how the "don't knows" might vote, CommunicateResearch asked people: "Generally speaking, do you think of yourself as Conservative, Labour, Liberal Democrat or other?" Those who are not likely to vote at a general election were not included in the figures.
The results of the "party identification" question show that Labour is struggling to retain the backing of its natural supporters.
It will increase fears among Labour MPs that the Government is "drifting" as Tony Blair completes his final months as Prime Minister amid bad publicity over the "cash-for-honours" affair and the problems engulfing John Reid, the Home Secretary.
Some 82 per cent of those people who regard themselves as natural Tories intend to support the party in a general election - the highest "core vote" rating of the three main parties.
It is a sign that David Cameron is winning over his party's traditional supporters, despite some reservations about his drive to reposition the Tories on the political centre ground.
The Liberal Democrats have the backing of 80 per cent of their natural supporters. In contrast, Labour has the support of 64 per cent of its core voters.
Mr Cameron's modernisation drive appears to be winning over floating voters who identify most with other parties. Some 15 per cent of Labour identifiers say they will vote Tory and a further 11 per cent intend to back the Liberal Democrats. Meanwhile, 11 per cent of those who identify with the Liberal Democrats say they will vote Tory and 3 per cent that they will back Labour.
The overall party ratings will come as a relief to the Liberal Democrats, who have bounced back after a period in which they appeared to be making little progress, and the Tories, who trailed Labour by one point last month.
CommunicateResearch found that Labour is more popular among women than the Tories. Mr Blair's party (31 per cent) holds a narrow lead over the Tories (30 per cent) among women, while the Tories (39 per cent) are more popular than Labour (27 per cent) among men.
The Tories (33 per cent) are just ahead of Labour (32 per cent) in northern England. Mr Cameron's party also enjoys a lead in the South-east, the Midlands and Wales and the South-west while Labour is ahead in Scotland.
The Tories are ahead in the top three social class groups (AB, C1 and C2s) with Labour holding the advantage only among the bottom DE group.
The rising level of support for other parties will worry the mainstream parties. The Green Party and the Scottish National Party are on 3 per cent each, UKIP on 2 per cent, the British National Party on 1 per cent and Plaid Cymru also on 1 per cent.
CommunicateResearch telephoned 1,008 adults between January 26-28. Data was weighted to take account of expected turnout and party identification for those who declined to say how they would vote. CommunicateResearch is a member of the British Polling Council and abides by its rules.
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