Nigel Farage has hinted that more MPs could follow Douglas Carswell by defecting to his party before the election.
The Ukip leader said politicians among the Conservative and Labour ranks "feel strongly" on the issues the party stands for.
"I don't think anybody will say that Douglas Carswell coming to Ukip is a one-off.
"There are many other people out there that are making up that calculation now," he added.
The rebel Conservative MP Douglas Carswell delivered a double blow to his party today - a shock defection to Ukip and he has forced a by-election in Essex which many believe the Tories are likely to lose.
The deeply Euro-sceptic Mr Carswell, who is the MP for Clacton, was unveiled as Ukip's newest recruit in a press conference in London. He said he was defecting from the Tories because Mr Cameron was not serious enough about the change needed in Britain's relationship with Europe.
He will resign as an MP when Parliament returns next week, forcing a by-election which could see him returned as Ukip's first ever elected member of parliament.
Click below to watch a full interview with MP Douglas Carswell:
Prime Minister David Cameron has described Tory MP Douglas Carswell's defection to UKIP as "deeply regrettable" and "self-defeating".
William Hague has said Douglas Carswell's decision to defect to Ukip is "totally counter-productive" because only the Conservatives can offer the public a choice on EU membership.
The Leader of the Commons said: "It's a totally counterproductive thing to do, of course, because the only chance of real change in Europe, the only chance of having a referendum where people can decide to say in the EU or leave the EU is having a Conservative government."
Backbench Tory MP Mark Pritchard agreed with Mr Hague, saying Mr Carswell had made an "error of judgment" that would end up helping Labour in the 2015 general election.
Defecting Conservative MP Douglas Carswell says he want to "shake up" the Westminster "clique" with his move to Ukip.
Carswell said the Conservatives' failure to take a stand against the European Union was at the heart of his decision.
ITV News Political Correspondent Libby Wiener reports:
Ed Miliband has tweeted that Douglas Carswell's defection show the Conservatives are "too divided to stand up for hard-working families".
Douglas Carswell’s defection is not just a blow to David Cameron. It shows the Tory Party too divided to stand up for hard-working families
A Conservative MP in Essex is calling for more clarity on Europe from the Tory leadership following the defection of Clacton MP Douglas Carswell to UKIP.
John Baron, the MP for Basildon and Billericay said: "I'm sorry that Douglas is leaving us. Every MP must make their own decisions about these matters but I do think it will yet again focus the Conservative Party and indeed the country on getting our relations right with the EU."
Mr Baron said he would stay in the Conservative Party but he is calling for more clarity on which powers the party would like to repatriate if they win the next election.
A senior Tory in Douglas Carswell's Clacton constituency has said news of his defection to Ukip has come as a "bolt from the blue".
Mick Page, the leader of Tendring District Council, which covers Clacton said: "That's come as a shock - a bolt from the blue."
Speaking to the Press Association he added: "We always thought he was a Conservative very much against Europe but we thought he would work within the party to achieve his aims. As far as I'm aware the Conservative association had no warning of this."
Douglas Carswell has said he is leaving the Conservative Party because too much of the leadership "aren't serious about the change that Britain so desperately needs".
The Clacton MP says too many Conservatives "talk the talk" on key issues at elections but have not done enough to make change happen.