Conservatives have warned Douglas Carswell he will live to regret his decision to defect to Ukip, following the Clacton MP's bombshell announcement on Thursday morning.
Carswell, one of parliament's most eurosceptic voices, surprised Westminster today by revealing he was joining Nigel Farage's party and would trigger a by-election in order to become the Ukip's first ever elected MP.
David Cameron said Carswell's defection was "deeply regrettable" and "self-defeating". And Tory MPs have hit out at their former colleague, accusing him of damaging the prime minister's chances of securing the majority in 2015 he needs to deliver on his pledge to hold an in/out referendum.
Andrew Bridgen, a staunch eurosceptic, told The Huffington Post that he wished the "free thinking and independent minded" Carswell had stayed to fight for his views within the Tory party. "He may well regret it in my view," he said. "Douglas may regret it because I don't think Farage necessarily likes people like Douglas. Farage wont want the competition. Farage runs a one-man-band, he is bit of a demagogue."
The North West Leicestershire MP added that he had not seen Carswell's announcement coming: "I was shocked. As someone who is a friend of his and that I am close to politically I had no inkling. I was aware he was very concerned about the rise of Ukip in his own seat."
Senior backbencher Bernard Jenkin, who is an Essex neighbour of Carswell, also told the BBC that the defection had come as a "bolt from the blue".
"Douglas will regret making this move because the more Tory voters defect to Ukip, the more likely it becomes that Ed Miliband becomes prime minister," he said.
And Northampton South MP Brian Binley, who would vote to leave the EU, said Carswell had shown "poor judgement" by joining Ukip.
"I don't think his decision is based on good judgement. Douglas is a very intelligent guy with lots of brains in his head but it appears there was no room for judgement," he told HuffPost. "To now make a theatrical gesture at a time when we [the eurosceptics] have got a lot of what we want, and to make it more difficult, seems absolutely crazy."
Farage welcomed Carswell to the party and described him as "just about the most perfect fit". He also commended his actions as the "bravest, most honourable and noblest" he had witnessed in British politics during his lifetime. He added: "I don't think it is any great secret there are now a number of MPs sitting on the Conservative benches and indeed some now sitting on the Labour benches who hold Ukip's views very strongly."
Wyre Forest MP Mark Garnier, whose mother was a founding member of Ukip, admitted Carswell's defection was a "very big deal" but dismissed the suggestion that other Tory MPs would would follow Carswell's lead as "massively hyped up".
He told HuffPost: "He doesn't have the following of many backbenchers. He always been outlier, always been someone who comes along with sightly selectively argued points don't necessarily make a huge amount sense under strict scrutiny," he said.
Carswell's decision sent shockwaves throughout the Tory ranks. Local councillor Steve Tierney, chairman of Wisbech Conservatives in Cambridgeshire, said: "I fear he'll regret the decision as I think it's going to jar for him when he starts out at Ukip. They are nothing like the libertarian image that they put out to the nation.
"Many of the policies they push are more authoritarian have a dark side to them. They have no bearing on the image they claim to have."
Reacting to Carswell's decision, another Tory MP told HuffPost: "He doesn't have much a sense of humour, he takes life terribly seriously."
Carswell was first elected to parliament in 2005 and has been leading voice on the eurosceptic wing of the Tory party. His defection this morning was kept secret, with even Ukip press officers seemingly not aware of what was about to happen.
He said while he thought the prime minister was a good man, he was "just not serious about the change we need", including his desire to leave the European Union.
"If I genuinely believed the Tory leadership were moving my way on this I would not be here. David Cameron has made up his mind, he wants to stay in. It's all about positioning for the election," he said. "We need change. People have a right to expect a government which answerable to Parliament and a Parliament which accountable to people."
Carswell won a 12,068 majority in 2010. If he is successful in holding on to his seat he will become Ukip's first ever elected MP. In 2008 Castle Point Tory MP Bob Spink defected to Ukip. He fought the 2010 election as an independent, but lost.
On Tuesday, Farage was selected as Ukip's candidate to fight the Kent seat of Thanet South. Speaking in Ramsgate after his selection, Farage said he believed Ukip could hold the balance of power after 2015.
Ed Miliband said: "Douglas Carswell's defection is not just a blow to David Cameron. It shows the Tory Party is too divided to stand up for hard-working families."
Asa Bennett contributed to this report.