Cameron faces new EU referendum backlash

Opinion polls released over the weekend suggested that Carswell will hold his Clacton seat in Essex, a region where Ukip topped the poll in May's European elections, as Ukip's candidate by a margin of more than 40 points over the Conservative candidate.

Ukip has prioritised 12 seats, most of them currently held by Conservatives, as it tries to make its first breakthrough into the Westminster parliament, even as Conservatives fear that a surge in support for the anti-EU party would lead to Labour, which does not support an EU referendum, winning next May's election.

For his part, Cameron has promised to renegotiate the UK's EU membership terms followed by an in/out referendum in 2017 if the Conservatives win next year's election. He, and the majority of his ministers, have maintained that they would vote to remain in a reformed EU.

Meanwhile, a survey of more than 3,200 businesses across the UK found that six in 10 felt that a British exit would damage the country's economic prospects, although they supported renegotiation of the UK's membership terms.

Fifty nine percent of responding firms stated that leaving the EU would cause economic harm. Sixty percent believe that remaining in the EU while transferring specific powers back to Westminster would have a positive impact.

At the same time, 46 percent said that further integration with the EU would damage economic prospects.

“These results show that firms believe a renegotiated relationship with the EU, rather than further integration or outright withdrawal, is most likely to deliver economic benefit for the UK," said John Longworth, the British Chambers of Commerce's director general.

Companies were "frustrated by the slow progress of the single market in services," he noted.

For his part, Donald Tusk, the newly appointed European Council chief, said at the weekend that he would "certainly meet the concerns voiced by Britain", adding that many of Cameron's plans to reform the bloc were "acceptable to reasonable politicians in Europe."

"No reasonable person can imagine an EU without Britain," he said.