UK Prime Minister David Cameron has risked further alienating the grassroots of his Conservative Party by dismissing rival UKIP supporters as "some pretty odd people" on live television.

A poll on Saturday 5 January showed record support for UKIP could result in a Labour landslide at the next general election. Backing for the anti-EU party has risen from 3 percent in 2010 to 16 percent, according to a survey for the Mail on Sunday. Those numbers would cost the Tories 51 seats, handing Labour a Commons majority of 94.

Asked on the BBC's Andrew Marr Show whether he regretted branding UKIP voters "fruitcakes" and "closet racists", Cameron told Marr: "When you are prime minister, you have to get used to the fact that in the middle of a parliament, you're going to have people going in all sorts of directions."

He added: "You've just got to get on with the job in hand. There are some pretty odd people out there."

His remarks attracted immediate criticism, with Conservative Home blogger Tim Montgomerie calling his comments "un-prime ministerial".

Ahead of a key speech on Europe set for 15 January, Cameron insisted that Britain's national interest lay in remaining inside the EU. "The key point is that 50 per cent of our trade is with the EU," said Cameron. "Because we have a seat at the table, we can help write the rules. If we left the EU altogether, we'd have no say in the market into which we sell."

The president of the European Council, Herman Van Rompuy, has warned Cameron that attempts to "cherry-pick" policies could lead the union to unravel, while efforts to claw back powers from Brussels would jeopardise the future of the single market.

But Cameron insisted he had already managed to renegotiate key powers that had been handed to Brussels. "People told me it would never be possible to make changes," he said. "But I've already managed to get us out of the bailout power, where we had to spend money bailing out other countries. We're out of that."

He also highlighted the EU's Working Time Directive as "something that should never have been introduced", and said the Schengen border treaty and EU fisheries policies were other areas where he would seek to renegotiate.

UKIP leader Nigel Farage hit back, saying Cameron had been reduced to "begging at the top table" in Brussels for piecemeal changes.

"No matter what he says now, after so many broken promises, so many 'cast-iron guarantees', can anybody honestly believe that he will be telling the truth this time?" Farage told Sky News. "The simple fact is that he wants us to stay in the European Union no matter how it is configured.

"Mr Cameron says that he will offer a real choice in 2015. That choice exists already. Voters can support one of the three old parties, including the Conservatives that want to keep us tied down by Brussels and its regulations, or they can opt for UKIP, which gives a clear commitment to withdraw."

Cameron also vowed to stick by his gay marriage proposals, which have similarly proved deeply divisive among his core supporters. "I just happen to think it's right, and I say this as a Conservative," he said. "Marriage is a great institution, and I want it to be available for gay people too."

The poll for the Mail on Sunday showed Labour on 38 percent, the Tories on 29, UKIP on 16 percent and the Lib Dems on 11.