It is "incredibly unlikely" that David Cameron will win the general election outright and he will need Ukip MPs to deliver an in-out referendum on EU membership, Mark Reckless has insisted.
Mr Reckless, who successfully defended his Rochester and Strood seat this week after defecting, said the damage inflicted by his new party on the Tories next May would be "small if any".
But only Ukip was able to defeat Labour in its traditional heartlands, he added. The comments came as Mr Reckless addressed the Eurosceptic Bruges Group in the wake of his victory.
He said there was no "serious prospect" that the Prime Minister would secure a Commons majority.
"I think it is something of a conceit, that I understand the Conservative leadership has to maintain but I am not sure that necessarily all Conservative backbench MPs need to, that somehow it is a realistic prospect that the Conservative Party under David Cameron is going to get an overall majority at the next election," he said.
"I haven't thought that was a serious prospect since the Conservative Party went into coalition with the Liberal Democrats.
"And that is largely because that decision led to unity on the left and a significant increase in the Labour vote due to departing Lib Dems.
"How David Cameron and the Conservative-led government have governed over the last four and a half years has also tended, to put it mildly, to reduce the prospects of the Conservative Party being successfully returned at the next election."
Mr Reckless said the impact of Ukip's surge on Tory seats would be "small if any".
But he said the Heywood and Middleton by-election - where the party missed out by just 600 votes - showed the effect on Labour could be much more significant. "We can actually win seats in Labour areas from people who would never dream of voting Conservative," he said.