Ukip has spent £46,000 on a full-page newspaper advert in an attempt to ratchet up the misery for David Cameron.
The party has tried to woo discontented Tories with an 'open letter' from party leader Nigel Farage, after the row over grass-roots supporters being branded "swivel-eyed loons".
Farage described the reported comment of a senior Tory figure deriding activists as "mad, swivel-eyed loons" as "the ultimate insult".
"Only an administration run by a bunch of college kids, none of whom have ever had a proper job in their lives, could so arrogantly write off their own supporters," he said.
"Conservatives are used to a party that is patriotic, supports business and believes in aspiration. Today they are led by people obsessed with wind farms and introducing gay marriage and happy to open the door to 29 million Romanians and Bulgarians from January 1 next year."
"If you are a Conservative who supports the Ukip position that we should be an independent, self-governing nation, then your party now treats you with contempt."
Farage told Tory supporters to "put country before party" and join Ukip.
£46,000 is the listed price for a full-page advert in the Daily Telegraph, according to its website.
That is just less than the total cash donations it received in the first quarter of 2013.
Last week it was reported that the party was issuing a plea for more funds after its success in recent elections was not matched by an increase in donations.
It was also revealed that one of the party's biggest backers, businessman Demetri Marchessini, was the author of a book advising women not to wear trousers because of their "big bottoms".
Farage's latest intervention coincides with the return to the Commons of the Government's bill to legalise gay marriage - a major source of discontent among traditionalist Tories, who believe it encapsulates the way the leadership has lost touch with ordinary, grass roots supporters.Suggest a correction