Gordon Brown continues to suffer from the fallout of the 10p tax row as the Tories moved to a 21-year record 18-point opinion poll lead over Labour.
Despite heading off a backbench revolt by agreeing to compensate those worst hit by Budget changes, less than one in 10 voters believe the Prime Minister is leading a "united" party.
And with crucial local elections - including the London mayoral poll - less than a week away, the YouGov poll for the Daily Telegraph newspaper showed Labour trailing by 44% to 26%.
It is the biggest gap since shortly after Margaret Thatcher won a third term as PM in 1987 and would be enough to give David Cameron's Opposition a 50-plus seat Commons majority.
Internet pollster YouGov questioned 2,073 people between Monday and Wednesday for the poll, at the height of the row over the effect of tax changes on some of the country's least well off.
A potentially catastrophic Commons defeat had loomed until the Government announced on Wednesday that it had accepted demands for it to help some of those affected by new tax rates.
But the volatile mood on the Labour backbenches was again highlighted on Thursday when the dispute threatened to reignite over confusion about whether the compensation would be backdated.
Chancellor Alistair Darling had to reassure MPs that low paid workers would be compensated this year after Treasury colleague Yvette Cooper said only pensioners would get backdated help.
Rebel leader Frank Field reacted angrily to her "badly briefed" comments insisting that the PM had assured him the entire package would be backdated to the start of the current tax year.
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And he warned that MPs would not take kindly to any attempt to tamper with the deal which he had hammered out with ministers.
