David Cameron and Ukip's Nigel Farage traded blows across the Sunday morning chatshows, with Cameron calling UKIP "some pretty odd people."
Speaking to Andrew Marr on the BBC, Cameron was asked about his previous description of UK Independence Party members as "fruitcakes, loonies and closet racists".
Cameron retorted: "There are some pretty odd people."
Ukip's Nigel Farage, who was speaking on Sky News
Speaking to Dermot Murnaghan on Sky News, Ukip's leader Nigel Farage hit back Cameron's insult.
He said: "It shows how disconnected he is. If he wants to go on being rude about me and rude about Ukip well let him do it, we won't lose any sleep over it.
"I don't think there is any prospect of any deal with the Conservative Party all the while that man leads it, given the way he has behaved and his attitude towards us.
"Look, I would do a deal with the devil if it got us what we need, which is a free and fair referendum so that we in this country can decide who governs us."
Voters should be "in no doubt" they will be offered a "real choice" on Europe at the next election, Cameron continued on Marr's show.
"There is going to be a large negotiation in Europe. When I became Prime Minister, people said to me 'Don't worry, the one thing you won't have is any treaty changes in Europe'.
David Cameron: Refused to back down on his Ukip 'odd people' claim
"I think we have already had three. One we vetoed so we aren't involved in at all... and we have had two others.
"People should be in no doubt that the Conservatives will be offering at the next election a real choice and a real way giving consent to that choice."
Asked whether any vote could be delayed by five or 10 years, Cameron said: "No, no, that's not going to happen."
Speaking to Dermot Murnaghan on Sky News, Conservative Party chairman Grant Shapps, said it was a "mainstream British view" that more powers should rest in Westminster and not in Europe.
He said: "We are mid-parliament. People often during mid-parliament look to protest somewhere.
"In the past that has been to the Liberal Democrats but they are in Government of course now. Come the next election in two, two-and-a-half years time, people will be able to look at our track record, which will include having dealt with a large amount of deficit - some of the really big issues in this country, some of the really difficult decisions we have had to make to get this country back on track."