Professor Abigail Marks and Dr Sue Cowan from Heriot-Watt University, together with Dr Gavin Maclean from Edinburgh Napier University, found the WCA causes a deterioration in people’s wellbeing and mental health and, in the worst cases, can lead to thoughts of suicide.

People applying for the sickness and disability benefit Employment and Support Allowance (ESA) are required to undergo the highly stressful and demeaning WCA to determine eligibility and the level of support they’ll ultimately receive.

But the hated face-to-face tests are routinely carried out by unqualified, or inexperienced assessors working for private contractors, on behalf of the Department for Work and Pensions (DWP).

Professor Abigail Marks, from Heriot-Watt University’s Centre for Research on Work and Wellbeing, explains: “The work capability assessments are fundamentally discriminatory to people with Mental Health Conditions.

“It is unacceptable that healthcare professionals who act as assessors for the WCA, for example, physiotherapists, nurses, occupational therapists are not fully qualified or trained to assess mental health conditions, yet they seem to be able to override participants’ own GPs, community psychiatric nurses, and therapists.

“The WCA must be entirely redesigned, and focus on the potential barriers to work for both physical and mental health problems.”

The report also warns that WCA’s can make work experience, or other voluntary work, almost ‘impossible’ for people with mental health conditions, further damaging their prospects of returning to work.

Thirty individuals who had been through the WCA were interviewed for the study. Advocacy organisations, Citizens Advice Bureau and a former employee of Ingeus, one of the private Work Programme providers, were also interviewed.

Dr Gavin Maclean, research assistant at Edinburgh Napier University, said: “Many of the participants in the study found the experience of the WCA so damaging that they stopped engaging in work-based activity and did not return to it.

“This could further reduce their long-term employability and potentially increase their dependency on benefits.”

Dr Sue Cowan, assistant professor of psychology in the School of Social Sciences, said: “For people with severe and enduring mental health conditions, voluntary work may be as ‘good as it gets’, as one of our participants stated.

“This does not mean a failure to obtain more. Rather, it is a recognition that an individual is making a choice, and the current system does not recognise or support that in any way.

“The assumption that engaging in voluntary work means an individual is fit for employment should be scrapped; there has to be much greater flexibility about undertaking training while on ESA and much greater value must be placed on voluntary work and work-preparation activity.”

Dr Cowan also draws attention to the devolution of new welfare powers to the Scottish Parliament: “As control over the Work Programme and Work Choice is devolved to Scotland, the Scottish Government must develop better programmes that work in parallel with the benefits system, but are appropriate to people with mental health problems”, she said.

Ayaz Manji, policy and campaigns officer at the mental health charity Mind, said: “The findings of this report are concerning but sadly not surprising, as they reflect what we hear from people every day.

“People with mental health problems tell us that the current fit-for-work test causes a great deal of additional anxiety. We know the assessors rarely have sufficient knowledge or expertise in mental health, meaning many people don’t get the right outcome and then have to go through a lengthy and costly appeals process.

“The current approach is not fit for purpose and needs to be replaced by an open and honest conversation based on each person’s individual needs.”

Shadow Work and Pensions Secretary Debbie Abrahams vowed to scrap the assessments if Labour becomes the next government and replace them “with a holistic, person-centred approach”. The WCA “is not only unfit for purpose, but is causing harm to some disabled people”, she told the Independent.

The WCA has been proven time and time again to be grossly inaccurate, with many claimants overturning negative decisions following a mandatory reconsideration or appeal.

In fact, the latest figures published by the DWP show almost two-thirds of cases that reach the appeal stage or overturned in the claimant’s favour. Claimants must ask for a decision to be reviewed by the DWP before they can appeal to a social security tribunal.

This latest call for a complete overhaul of the WCA follows similar calls from mental health charities and the Commons Work and Pensions Committee, who urged the DWP to undertake a “fundamental redesign” of the system in 2014. The DWP has so far failed to heed these warnings.