Controversial fit-to-work assessments have raked in over half a billion pounds for private firms, Atos and Capita, according to analysis by The Mirror. Work Capability Assessments were implemented in 2010 by the Conservative government in a bid to encourage more people claiming benefits to return to work.

According to The Mirror, the money made by the two firms for conducting the assessments has risen steadily year-on-year since 2013, when Personal Independence Payments (PIP) replaced Disability Living Allowance (DLA). The newspaper says its analysis shows £7m was paid to the companies in 2013, £91m in 2014 and £198m in 2015. In the first 11 months of 2016, it says the two firms were paid £211m for conducting the assessments. The money apparently covered the face-to-face interviews, paper assessments as well as fees for GPs' reports.

However, the assessments have been fraught with controversy since their inception, with critics arguing that the tests put undue pressure on those who were not fit to return to work to do exactly that. At the most extreme end of the scale, research by Oxford and Liverpool universities, published in the Journal of Epidemiology and Community Health last year, found that there had been a marked increase in suicides and mental illness in those subjected to Workplace Capability Assessments, between 2010-2013.

Additionally, figures up to September 2016 revealed the unreliability of assessments. Over 60% of appeals made against PIP decisions at a tribunal were won by claimants.

Outsourcing of the assessments was criticised in a report by the Public Accounts Committee in March after it was revealed that the cost of one type of assessment had risen from £115 to £190.

The Department of Work and Pensions told The Mirror: "Payments to our providers reflect the amount of work they do for us.

"We introduced PIP to replace the outdated DLA system, and as we invite more people to claim PIP, claims have been steadily increasing quarter-on-quarter since summer 2015."

However, since introduction of PIP in 2013, 110,000 of the 526,000 assessed had lost their benefits, the Guardian reported.

An Atos spokesman said: "The Atos team undertake PIP assessments on behalf of the DWP and do not take a decision on a person's eligibility for PIP; that decision can only be taken by the DWP. Each assessment is carried out under the guidelines delivered by the DWP."

A Capita spokesperson said: "Capita carries out PIP assessments according to DWP guidelines and professional codes of conduct."

The news will put growing pressure on the government to rethink the controversial assessment, which it said earlier this year it would no longer require those with chronic conditions to undertake annualy. Shortly afterwards, the government announced it would consult on reforms to the assessments, which were also the subject of Ken Loach's Palme d'Or winning film, I, Daniel Blake.

According to The Daily Mirror, over half a billion pounds has been paid to private firms by DWP to carry out Fit to Work assessments