Respected British MP Douglas Carswell dealt a heavy blow to Prime Minister David Cameron on Thursday as he announced he was to leave the Conservative Party and join the UK Independence Party (UKIP).
But the eurosceptic party will have to wait for its first member in the House of Commons as Carswell said he will resign from parliament and stand in the resulting by-election in Clacton, south east England.
UKIP leader Nigel Farage, who flanked his new recruit throughout a press conference to announce his resignation, called Carswell's decision "the noblest thing I've seen in British politics in my lifetime".
The defecting lawmaker accused Cameron of misleading voters about his promises to claw back more powers from Brussels ahead of a referendum on Britain's membership of the European Union, which is set to take place if the Tories win next year's general election.
"My position became untenable," explained Carswell. "The Conservative leadership is not serious about change. "
He said that Cameron's advisers had told him that Britain will not vote to leave the EU in the event of a referendum, because "we will give them (the voters) just enough to persuade them not to".
Carswell has earned a reputation as a staunch eurosceptic and radical libertarian since he was first elected in 2005 in nearby Harwich.
He was at the heart of the succesful bid to remove Michael Martin as speaker of the House of Commons following the 2009 expenses scandal that rocked parliament.
Farage announced on Tuesday he was to run for parliament in next year's election after his party confirmed him as their candidate for South Thanet, close to Carswell's former seat.