Support for Labour has plunged by 10 points in the past month, and the party is now running neck and neck with the Liberal Democrats, according to a poll released today.
The dramatic slump in Labour's fortunes has allowed the Conservatives to pull 22 points clear, Ipsos Mori found.
While support for all the main parties has declined in the aftermath of the MPs' expenses scandal, Labour appears to have fared worst by far.
The Ipsos Mori poll put the Tories on 40 per cent, down one since the same survey last month.
But Labour was down 10 points, putting the party on the same support as the Lib Dems, who were down four on 18 per cent.
At the same time, support for minor parties has doubled in the past month to 22 per cent, including 7 per cent for the UK Independence Party, 6 per cent for the Greens and 4 per cent for the British National Party.
* Ipsos Mori interviewed 1,001 British adults by telephone between 29 and 31 May, weighting data to match the profile of the population.