Former prime minister Sir John Major has hit out at the "sheer nastiness" of Ukip as Nigel Farage's party appeared on course for another by-election victory.
Sir John said that Ukip was "profoundly un-British in every way" because of their views and voters were only backing them out of frustration with the economy.
Mr Farage said he is "confident" that Mark Reckless will become Ukip's second MP after Thursday's Rochester and Strood by-election.
Mr Reckless defected from the Tories to Ukip and hopes to echo the victory of Douglas Carswell, who won the Clacton seat in a landslide for his new party last month.
Sir John drew a distinction between Ukip's leadership and those who had supported the party, saying: "I think many of the people who are voting for them are doing so out of frustration at the ongoing difficulties of the recession, the belief that they are losing out and falling behind.
"That will fade away as the economy improves, and it is materially improving."
In a strongly-worded attack on Ukip, he told BBC1's Andrew Marr Show "the policies of Ukip, the direction of Ukip, is, it seems to me, profoundly un-British in every way".
He said: "They are anti-everything. They are anti-politics, they are anti-foreigner, they are anti-immigrant, they are anti-aid.
"I don't know what they are for, we know what they are against. That's the negativity of the four-ale bar, that's not the way to get into Parliament and not the way to run a country.
"So they may be elected because people are frustrated."
He said the generosity shown by the British people in responding to the Ebola appeal and Children in Need was a "counterpoint" to Ukip's "negativity".
"What a counterpoint that is to the negativity and sheer nastiness of much of what Ukip stands for," he said.
Ukip leader Mr Farage told The Sunday Telegraph that he was "confident but not complacent" that Mr Reckless would win, partly on the back of a collapse in the Labour vote in the seat.
"We are smashing the Labour vote to pieces. This is not a straight fight between Ukip and the Tories," he said.
David Cameron has warned that a Ukip win would put the country at greater risk of "insecurity and instability in our economy".
The Prime Minister warned voters in the Kent constituency that they risk becoming another notch on the bedpost of Mr Farage's party, who would celebrate victory with "a pint in the pub" but would not represent local people as well as Tory candidate Kelly Tolhurst.
Mr Reckless said Mr Cameron was an "archetypal establishment figure" who was not "serious enough".
In a Sunday Times interview, for which he posed in a chainmail vest, carrying a sword and shield, Mr Reckless attacked the Prime Minister's style of government, run by a "cozy cartel" from a "Downing Street sofa".
"I've never felt I haven't been able to get my point of view over to him," Mr Reckless said, but he felt the Prime Minister was not "serious enough" and didn't really mean what he said.
"I think he just quite likes being Prime Minister. He is an archetypal establishment figure."
He added: "The Prime Minister is much more comfortable with the civil service and establishment advisers than seeking change. When once asked why he wanted to be prime minister he said he thought he would be quite good at it.
"I mean, what does he want to achieve?"
Mr Reckless, who had to apologise after missing a Commons vote in 2010 because he had had too much to drink in one of Westminster's bars, said he had not touched alcohol for "a year or two" and felt "healthier and better" as a result.
"That was a very embarrassing incident," he said. "I apologised, said it wouldn't happen again, and it hasn't. Indeed, I have not drunk at all for a year or two."