The Prime Minister has not handled misgivings among the public over Britain's relationship with the European Union in a "sensible way", a Tory peer has said.
Speaking in the wake of Nigel Farage's Ukip party win in the Rochester and Strood by-election, former Conservative Party Chairman Lord Tebbit argued it "never made sense" to "abuse" Ukip supporters.
In 2006 David Cameron described Ukip members as ''fruitcakes, loonies and closet racists, mostly''.
Lord Tebbit said: "I think trying to bring the party together on this issue is a pretty tricky one. I think if I'd been Prime Minister I would have been accused of fuelling the divisions as well from a different angle.
"But I don't think that he has handled the misgivings of a huge number of people outside Westminster, I don't think he's handled their misgivings in a sensible way.
"The last way to persuade people to come back and support you is to abuse them as nutcakes and loonies and all the rest of it. That never made sense to me."
Lord Tebbit said Mr Cameron should have "made plain" much earlier that "there were clear limits to our integration, but of course that was impossible because of being in a coalition".
He also said the Prime Minister "should have understood" the Ukip threat.
He told BBC One's Sunday Politics: "Would I be attracted by Ukip as a young man? I think I would be attracted to a lot of what they are saying, but I think I would still feel that to deal with those problems it would probably be easier to regain control of the Conservative Party, as Margaret Thatcher regained control from the Wets."
Mr Cameron's position as Conservative Party leader, he added, would be decided by the outcome of next year's general election.
He said: "I don't think his leadership is at risk before the election. I think his leadership will be decided by whether or not he can win the election."
Asked if the Conservative's could win in 2015, Lord Tebbit responded: "Yes, everything is possible, but the odds against it are heavy at the moment. I think it's a very difficult situation. I think the likelihood is that neither of the major parties will have a majority."
On dealing with Ukip's rise, he added: "As party chairman, you can't do more than your Prime Minister allows you, I think it's very difficult for him."
Lord Tebbit's comments came as Ukip's first elected MP and Tory defector Douglas Carswell, said he did not expect any imminent defections.
The Clacton MP told the same programme: "I don't really expect any this side of Christmas. But who knows? I didn't make up my mind for certain until about three weeks before I announced it. So let's wait and see. But what's important is what the voters do and trying to get the voters to make the switch. Frankly, who cares what 650 MPs now do".