Ukip apears to be the main beneficiary of the Maria Miller affair, with the party soaring to a new poll high as the Conservatives drop several points.
The ComRes poll put Ukip on 20%, up four points on last month and its higher ever result from the polling firm.
The Tories were down three points to 29%, their lowest rating this year.
The Lib Dems went down two points to seven per cent.
Labour was unchanged on 35%.
If replicated at the general election, the results would give Labour a majority of 74.
The re-emergence of the expenses scandal could not have come at a worse time for the Conservatives, as they ready themselves for what is expected to be a humiliating local and European election battle next month.
Privately, Conservatives have all but given up on doing any better than third place in the European poll, with Ukip still holding out hope of slipping into first place.
It is traditional for political parties to downplay their chances at election time, but the fears over the European election are substantiated by polling which suggests the Conservatives will hemorrhage support to Ukip.
A 'poll-of-polls' by University of Strathclyde professor John Curtice put the Tories on 23%, in third place, and the Lib Dems on nine per cent, in fourth place.
Ukip are on a 28% average, three points behind Labour on 31%.
A good month of campaigning could still see the Ukip leader win the top spot, humiliating both David Cameron and Ed Miliband.
Such a result would be disasterous for Labur's credibility ahead of the general election, but it would be even worse for the Conservatives, with many fearing that it would encourage Tory voters to continue lending Ukip their vote even at general election time.
Even if Ukip had just eight per cent support in 2015, it could be enough to split the Tory vote and deprive them of the keys to Downing Street.
The ComRes poll found 62% believed Cameron had shown a "serious lack of leadership" over his handling of the Maria Miller affair, with only 15% disagreeing.
Nigel Farage enjoys seven per cent more support than in Febuary, with appproval ratings of 27%