Survey of 26,000 voters suggests Tories would lose 83 MPs with swing of 6.5 per cent to Labour.
UKIP has surged into second place but it won't be troubling Labour next Thursday.
After a Tory strategist claimed a private poll put them two points ahead of Labour in marginal seats, the party comes under pressure to release its findings.
Labour has a 14-point lead in the 32 most marginal Tory-Labour seats, while the Lib Dems are just three points behind the Conservatives in the eight most competitive Tory-Lib Dem seats.
A survey by Lord Ashcroft shows 12% of the trade union's 1.42 million members would affiliate themselves to Labour under the new system but also that they oppose large donations to the party.
Expect Conservative rebels to seize on the finding as proof that the party could be performing better under an alternative leader.
Labour would win a majority of 84 by gaining 93 seats off the Tories and 13 off the Lib Dems. But remember: it's a snapshot, not a prediction.
A new poll from Lord Ashcroft shows seven per cent of Lib Dem voters and 10 per cent of UKIP voters expect to vote Conservative at the general election.
The Conservative peer and former deputy chairman on his fascination with polling and why Tory modernisation must continue.
He's one of the Tories’ least understood assets. By pouring money into polling, he has given the party one of its most lethal weapons — but now will Michael Ashcroft unleash his power over information to destroy Cameron?