Cameron to take 200,000 off 'incapacity' benefits

He will risk the wrath of disability charities by promising that if elected, he would order a full medical inspection for every one of the 2.6million who are registered as too ill to work.

Those deemed well enough to return to work would be forced to accept ordinary unemployment benefit – worth £20 a week less.

The Tories estimate that at least one in ten of those claiming to be unfit – or more than 200,000 people – is well enough to return to work.

The proposal is part of far-reaching welfare reforms to be unveiled by Mr Cameron in Brixton, South London.

They include greater use of private companies to retrain the long-term jobless – and forcing single mothers to find part-time work when their youngest child reaches four.

Shadow Work and Pensions Secretary Chris Grayling said: "It is time to take tough action against those who are deliberately staying at home and claiming benefits rather than going back into work.

"If you get a reasonable job offer, you should take it – if you don't, you can't expect to carry on claiming benefits."

He said that Labour had failed to reform incapacity benefit, in particular shying away from reassessing existing claimants, many of whom had been out of work for decades.

But Work and Pensions Secretary Peter Hain said: "They have been promising radical new welfare policies for months. Instead, they are plagiarising plans announced by us and seeking to present them as their own.

"Unlike our fully funded and deliverable programme, the Tories have no credible plan to fund this expansion in welfare-to-work."