MP Douglas Carswell Quits Tories For UKIP
Conservative MP Douglas Carswell has announced he is defecting from the Tories and joining UKIP.
The MP For Clacton in Essex said he made the decision because he believes UKIP is the only party that can break up the "cosy Westminster elite".
Flanked by his new party leader Nigel Farage, Mr Carswell was cheered by supporters as he said he would take the unusual step of resigning from Parliament and fight to win back his seat for UKIP in a by-election.
Mr Farage told his latest recruit: "I think what you've just done is without doubt the bravest, most honourable and noblest thing I've seen in British politics in my lifetime."
Mr Carswell was scathing in his criticism of David Cameron and his Government - accusing the Prime Minister of being insincere in his vow to reform Britain's relationship with Europe.
He said he had not told the PM of his decision to vacate the seat - which has a Conservative majority of more than 12,000 - in advance.
Speaking to Sky News moments after the announcement, he said: "I don't think they're serious about the change this country needs. This country needs serious political reform.
"They're not serious about making government accountable to Parliament and Parliament accountable to the people."
He added: "I know David Cameron is not serious because I've heard him say it."
He admitted that he could lose the by-election but said he would trust the voters to make their own decision.
Nigel Farage insisted Mr Carswell was not the only sitting MP who backed his policies.
He told Sky News: "I've spoken to people in the Conservative Party and the Labour Party who do not want Britain to be borderless, who think this is doing great damage to the working opportunities of people in Britain.
"I don't think Douglas Carswell is going to be considered an isolated eccentric - there are other MPs out there considering their options."
Speaking to the BBC in Glasgow, where he is due to give a major speech on the Scottish independence referendum, David Cameron said Mr Carswell's decision was "deeply regrettable" and "self-defeating".
Tory MP Bill Cash - a standard-bearer for the eurosceptic cause - told Sky Mr Carswell's move was a "monumental misjudgement".
Sky News Political Editor Faisal Islam said: "This is precisely the sort of move that turns what might have been called a protest vote in May into something more substantial.
"Douglas Carswell is known for his views on Europe but he's also popular for a variety of reasons.
"The Prime Minister's up in Glasgow trying to keep the Union together and now he's trying to stitch his party together.
"And the old Conservative problem of Europe raises its head again, at the worst possible time."
(c) Sky News 2014