Conservative Cabinet minister Ken Clarke has said that UKIP's politicians are "clowns" with no "positive" policies.
His comments came as the party accused the Tories of conducting a "morally reprehensible" smear campaign against its candidates in this week's local elections.
Speaking to Sky News' Murnaghan programme, he said: "It's very tempting to vote for a collection of clowns or indignant, angry people who promise that somehow they will allow you to take your revenge on the people who caused it.
"You should actually vote for people who you think are going to be sensible county councillors."
The Transport Secretary has said Ukip candidates are being put under the same scrutiny as those from other parties as the party accused the Tories of a smear campaign.
Patrick McLoughlin told BBC One's Andrew Marr Show. "Candidates are always put under scrutiny and I think it's right. Why should Ukip candidates get away without any scrutiny when other parties have scrutiny as far as their candidates are concerned?"
"I don't know anything about a smear campaign."
Asked whether it was right to trawl through would-be councillors' social media accounts, he said: "I don't know whether that's happened, I'm just saying it happens to all parties and candidates are put under scrutiny."
Godfrey Bloom, a senior UKIP MEP, has complained via a series of leaked emails that forging Ukip's policy platform is like "herding cats", insisting senior figures needed to learn to toe the line.
In a series of exchanges with Treasurer Stuart Wheeler, leaked to the Observer, Bloom warned that "some quite senior party members are going to have to stable their hobby horses".
"Having worked on the defence paper for over one year it would appear Ukip has more military and naval experts than we have soldiers," he wrote.
"Most of them do not agree with each other. It is like herding cats.
"We are also attracting new members who bring main party 'baggage'. Focus groups, quotas, even political correctness. We must be wary of listening to these siren voices. We did not get where we are today by following, but leading."
The MEP said he had been in talks with free market think-tanks including the Institute of Economic Affairs and Civitas, and suggested Ukip could buy their policies "off the shelf" where they are close to "our own small government, low tax, libertarian position".