David Cameron has been told in private by Tory Eurosceptics that the Conservative party will split in half after the general election if he fails to renegotiate Britain's EU membership terms to a Common Market-style trade-only deal.
In a sign of the threat facing the prime minister, the Eurosceptics have made clear that a sizeable body of MPs at all levels of the party will campaign for an EU exit vote in his planned referendum in 2017 if he sticks to his current negotiating plan.
Cameron is hoping to negotiate an opt-out from the EU's declaration to create an "ever closer" union and to create safeguards for Britain and other countries outside the eurozone when rules are drawn up for the single market. He is also aiming to impose travel restrictions on citizens from new member states and to introduce tougher rules on benefits for EU citizens.
Hardline Eurosceptics are making clear his plans fall far short of their aims of ending Britain's political relationship with the EU by downgrading membership to something more akin to a customs union, though they are also insisting they have no plans to follow the example of Douglas Carswell, who defected to Ukip on Thursday.They are saying that they intend to remain in the Conservative party to demand a tougher negotiating stance and to campaign for a no vote in the referendum from within the party if their demands are not met.
Ukip, meanwhile, has sought to build on the momentum of the defection of Carswell, who cleared the way for a byelection in his Clacton constituency on 9 October by formally resigning his seat. The party is suggesting there could be eight more defectors. Stuart Wheeler, the former Tory donor who bankrolls Ukip, said he had hosted a series of Tory MPs for lunch in Mayfair. Ukip also suggested Eurosceptic Labour MPs might jump ship.
Conservative whips are confident that no further Tory MPs are planning to defect. They are aware of the messages that have been passed on from the Eurosceptics, suggesting a showdown after the general election and before the referendum.
Austin Mitchell, the most prominent Labour opponent of Britain's EU membership, told the Guardian he has not been approached by Ukip. "I'm probably too old to be approached," the veteran MP for Great Grimsby said. "But all Labour MPs are focused on getting Labour back into power."
Cameron accused Carswell of making a "quite bizarre" decision to defect, saying the move would help Labour win the next election. He said it was "odd" and self-defeating for such a staunch Eurosceptic to stand down as MP for Clacton and reject the only party that had a realistic chance of staging a vote on EU membership.
Asked by the Guardian during a visit to Scotland whether the Ukip crisis would bolster a yes vote for Scottish independence, Cameron said: "[Carswell] stood as a Conservative in 2010 when we weren't promising a referendum and he's left the Conservative party when we are promising a referendum. For someone who wants a referendum, it's a rather strange way to behave."
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