A surge in support for the UK Independence Party has pushed it to within just two points of the Conservatives in a poll of voting intentions.
In a fresh headache for David Cameron, the survey by Survation showed a five-point slump for his party to a record low for the pollster of 24%.
It was released as the Prime Minister wrote to Tory activists in a bid to smooth fraught relations with the grassroots over Europe and gay marriage.
The poll was partly after the storm erupted over reports that a close ally of Mr Cameron branded Tory activists "swivel-eyed loons".
Nigel Farage's rampant eurosceptic party has jumped six points since the start of the month - days before it scored dramatic local election wins - to 22%.
Labour slipped one point to 35% but saw its lead over the Tories stretch to 11 points. The Liberal Democrats were down one point at 11%.
Survation's findings - based on 1,000 responses from an online panel - were calculated using a weighting system to reflect a number of factors including individuals' stated likelihood to vote.
It also showed an eight-point rise to 30% since January of those intending to back Ukip in next year's European Parliament elections, with the Tories down four points at 20% and Labour unchanged on 30%.
The split of public opinion over Britain's EU membership remained stable since the start of the year however - 50% backing exit, 36% preferring to stay in and 14% undecided.
Meanwhile, a second poll taken in the wake of the "loongate" allegations showed a sharply different result, with Conservatives recording a relatively comfortable 17-point advantage over Ukip.
The YouGov survey for The Sun put the Tories on 31% and Ukip on 14%. Labour on 39% had an eight-point lead over the Conservatives, while the Liberal Democrats were trailing on 10%.
Unlike Survation, which asks respondents whether they would vote for Conservatives, Labour, Lib Dems, Ukip or "Another Party", YouGov's poll prompts participants with the names of the three traditional major parties, listing Ukip under "Other parti