The Conservative lead over Labour has slipped to nine points in the third poll this weekend to suggest the election could result in a hung Parliament.
A BPIX poll for The Mail on Sunday put David Cameron's party on 39 points, Labour on 30 and the Liberal Democrats on 18. It followed two surveys yesterday showing Labour had narrowed the gap to seven and nine points.
If repeated at an election, all three polls would leave the Tory leader short of an overall majority. It comes amid speculation of a rift between Mr Cameron and George Osborne after the party leader, in a speech at the World Economic Forum in Davos, said Tory plans to axe state spending would not be "particularly extensive".
But confidence in Labour circles will be dented by reports of a new book said to contain damaging revelations about Gordon Brown.
Downing Street furiously denied a claim in The Mail on Sunday that the Prime Minister hit a senior male official. The claims are linked to a new book on the fall of New Labour by political journalist Andrew Rawnsley, entitled The End of the Party. But it was not clear last night that the accusation that Gordon Brown punched someone is in the book, or whether the author had merely investigated rumours.
A Downing Street source said: "The idea that the Prime Minister hit someone is absolute nonsense."
The book is, however, expected to contain other allegations of Mr Brown's bad temper, including claims he swore at staff after he was "snubbed" by President Barack Obama during a visit to the US last September.