Former Conservative MP Quentin Davies has launched a strong attack on David Cameron at the Labour Party conference.

Davies, who defected to Labour earlier this year, claimed the Tory leader has no "strategy" or "conviction", in contrast to Gordon Brown.

Invited onto the main conference stage by Labour deputy leader Harriet Harman on Monday, the Grantham MP won strong applause for having crossed the floor of the Commons and a rapturous welcome for his short speech.

In it, he invited other "one nation" Tories, which he said referred to support for a strong economy, social justice and internationalism, to "take the plunge" and join Labour.

He said the Conservatives had abandoned this tradition in favour of a return to the Right in recent years.

Davies accused Cameron of engaging in "a Faustian pact with his own extremists".

He added that the Opposition leader was unfit to be prime minister because he said "such consistently foolish and superficial and transparently contradictory things".

"They may have tactics, they have no strategy," Davies told delegates. "That is a fatal flaw in political life.

"David Cameron has the most expensive spin doctors in the business. He pays Andy Coulson and Steve Hilton between them some £500,000 a year.

"But I have to say to David Cameron: you can't buy convictions from a spin doctor. You can't buy them from anyone. You either have them or you don't. And if you don't you're wasting your time in politics.

"You need before you go into politics to have a clear vision of what you want to achieve, a clear vocation for your country and stick consistently to that. The Labour Party has that vision. It is the authentic one nation vision of our time.

"And our doors are open and our hands our outstretched to every man and woman in the country who shares that vision and who wants to join with us to bring it to fruition."