The Tories have slumped to a 14-point deficit behind Labour, according to an opinion poll published in the Sunday Express.
The survey puts David Cameron's party on just 29% - compared to 43% for Labour.
The paper said that it represented Labour's biggest lead over the Conservatives for the decade. The last time support for Labour peaked this high was in December 2002 when Tony Blair was in Downing Street and Iain Duncan Smith was the Tory leader.
The poll findings also make grim reading for Mr Cameron's coalition partners, the Liberal Democrats, who are on just 9% - level pegging with the UK Independence Party.
Angus Reid surveyed 2,026 people on 8 June.