Tory Shadow Work and Pensions Secretary Chris Grayling said: “It’s no good the Government leaving these people to remain on benefits for the rest of their lives. We need a firm but fair approach that gets them back into work.”

Claimants can qualify for incapacity benefit if they are diagnosed with the medical condition “reaction to severe stress”. They must also face a medical test of incapacity for work, which is known as the Personal Capability Assessment.

But that has not deterred the growing number of claims for handouts. The UK has one of Europe’s highest proportions of people on incapacity benefit.

It is also feared the benefits system is open to abuse. Earlier this year a welfare adviser revealed how fewer than a third of claims are legitimate.

Investment banker David Freud, who produced a Government report welfare policy, warned that up to 185,000 claimants work illegally while on the benefit.

But the Department for Work and Pensions insisted that the number of people claiming incapacity benefit was at its lowest level since 2000.

“People don’t automatically get incapacity benefits because they suffer from severe stress,” said a spokesman. “We look at the impact a condition has on a person’s ability to work and there are strict checks in place.

“We’re overhauling the whole system of incapacity benefits to place the emphasis on what work people can do, not what they can’t.” He said Work and Pensions staff were adopting a new policy aimed at helping people with mental health problems – such as severe stress – to get back into work.

“Mental health conditions have, by and large, replaced bad backs and similar conditions as the main reason why people claim incapacity benefits,” he said.

“This is because of better recognition of these health problems and a reduction in people who do heavy manual work.”

But Matthew Elliott, of the TaxPayers’ Alliance campaign,  hit out at the rocketing levels of state payments.

“Too many people who are able to work are either wrongly signed off or are being allowed to malinger at the taxpayer’s expense,” he said.

“It's no good for taxpayers, the wider economy or these individuals for tens of thousands of people to be put on the scrapheap when they could be helped back to work.”

He added: “What you have to ask is, why have the numbers of people with stress gone up? Are people’s lives now more stressful? It is difficult to see why they should be.” Mr Elliott also attacked the current assessment system and called for changes which would relieve the pressure placed on medical professionals, who must make crucial judgments on claimants’ conditions.

“The problem we have at the moment is that people are being signed off by doctors far too easily,” he said.

“If you go to a doctor, saying you are stressed and unable to work, and the doctor does not accept your diagnosis, they are  effectively calling you a liar. That puts doctors in an impossible position.”

He added: “Surely a better system would be to have Government-approved doctors to assess the worth of people's claims.

“It would not be just for stress but all the other medical reasons which people give for making them unable to work.”