The Tories could be on track for a surprise victory in the Eastleigh by-election, according to a poll on Saturday night.
Research by Survation for the Mail on Sunday put the Conservatives' Maria Hutchings on 33% - four points ahead of the Liberal Democrats.
The figures reverse recent findings that suggested Nick Clegg's party would narrowly retain the seat vacated by disgraced former Cabinet minister Chris Huhne.
However, the advantages are within the pollsters' margin for error - suggesting with less than a week left the contest is going to the wire.
The UK Independence Party also appears to be performing well, with the latest survey giving its support as 21%. There are reports locally that the party is taking votes from the Lib Dems as well as from the Tories.
However, Ukip did suffer a blow on Friday night when one of its MEPs, Marta Andreasen, announced she was defecting to the Conservatives.
Labour is trailing on 13%, the poll found.
Survation questioned a representative sample of 543 adults in Eastleigh between February 19 and 22.
Bookmakers William Hill cut the Tories from 9/2 to 7/2 to win the Eastleigh by election after the shock poll.
The Lib Dems have been lengthened from 1/6 to 3/10 favourites, and UKIP shortened from 12/1 to 8/1. Labour have drifted out to 50/1.
William Hill spokesman Graham Sharpe said: "Suddenly, the red hot favourites are on the drift. As so often is the case, a by election is producing an unexpected turn of events."