LONDON (Reuters) – British Prime Minister David Cameron suffered a setback on Thursday when a lawmaker from his ruling Conservative party unexpectedly defected to the UK Independence Party (UKIP) party, which wants Britain to leave the European Union.

The move, by Douglas Carswell, a Eurosceptic, comes eight months before a national election in which UKIP threatens Cameron’s re-election chances. UKIP won May’s European elections in Britain after taking votes from the Conservatives.

Carswell, 43, said he was standing down as a Conservative member of parliament with immediate effect because he had lost faith in Cameron’s promises to try to renegotiate Britain’s EU ties if he wins power again next year.

Cameron has said he would give Britons an in/out EU membership referendum in 2017 after the renegotiation, if it happens.

“David Cameron has made up his mind, he wants to stay in (the EU),” Carswell told a news conference.

“It’s all about positioning for the election. If I believed they were sincere about real change I wouldn’t be here, I don’t believe that they’re serious.”

UKIP, which wants an immediate British EU withdrawal and an end to what it calls an “open door” immigration policy, has no seats in the British parliament, but 24 of the country’s 73 seats in the European Parliament.

A Conservative spokesman said Carswell’s defection was “regrettable”, saying the Conservatives were the only party that could deliver an EU membership referendum.

The announcement threatens to unsettle the Eurosceptic wing of Cameron’s party, estimated to account for around a third of his 304 members of parliament, ahead of next year’s national election and could prompt other defections.

Internal Conservative party ructions over Europe contributed to the political undoing of the last two Conservative prime ministers, John Major and Margaret Thatcher.

‘HAMMER BLOW’

Michael Dugher, a lawmaker from the opposition Labor party, which is ahead in opinion polls before next year’s national election, said Carswell’s defection was “a hammer blow” to Cameron.

“Confidence in David Cameron is collapsing inside a Conservative party which is divided and running scared of UKIP,” Dugher said in a statement.

Nigel Farage, UKIP’s leader, said he hoped Carswell’s decision, which he praised as “noble”, would embolden other members of parliament to switch sides.

“I don’t think it’s any great secret that there are now a number of members of parliament sitting on the Conservative benches, and indeed now some sitting on the Labor benches who hold UKIP’s views very strongly,” he said.

“It will be an encouragement to others.”

The defection gives Cameron, who is due to appear in Scotland later on Thursday, a short-term political problem.

His party now faces an election battle in the coming months for Carswell’s parliamentary seat in Clacton, southern England, a constituency which Matthew Goodwin, an academic at the University of Nottingham, said UKIP was likely to win.

“The demographics in Clacton are ideal for UKIP,” he told BBC radio. “This is a struggling, coastal seat, lots of older, white voters, few minority voters – it’s classic, ‘left-behind’ territory,” he said.

Carswell, who comfortably took that seat in 2010 with a majority of more than 12,000 votes, said he would try to win it again, this time to represent UKIP.

Carswell accused Cameron and his party of being filled with self-interested cliques who were more interested in possessing power rather than effecting real change.

“Ultimately they’re more comfortable being a small clique in Downing Street, sitting on a sofa,” he said, referring to the street where Cameron’s office is located.

“For them politics is about people like them, it’s a game between different cliques to get to sit on the sofa.”

(Additional reporting by Stephen Addison, Michael Holden and Belinda Goldsmith; Editing by Angus MacSwan)