The parents of a man who suffered from epilepsy and died after being stripped of his benefits have blamed his death on the stress of being found 'fit for work'.
Colin Traynor, 29, was marked as being able to work as part of the government's overhaul of the welfare system.
He appealed against the decision but died before finding out the result which was ultimately successful.
His family learned the appeal verdict five weeks after his death in April.
Mr Traynor's father Ray said: "I firmly believe - 100% believe - that the system this government introduced has killed my son."
Mr Traynor told Channel Four News the appeal process should have been carried out more quickly, which would have eased his son's stress.
He criticised the bureaucracy which he believed led to delays in hearing the appeal.
"I don't want some government minister telling me what he can do, some penpusher in London - they don't even know my son, they've no idea whatsoever," said Mr Traynor, from Oldham, Greater Manchester.
"You've got to change the system we've got today. You've got to stop other people going through this.
"The assessment is wrong. There are other people like my son out there with different illnesses, and they are going through the same (thing).
"People are dying."
The original work capability assessment was carried out by the French firm Atos, which has sparked anger with some of its controversial decisions to judge people fit for employment.
But ministers believe the new system is fairer in deciding what sort of work claimants can perform.
A Department for Work and Pensions spokeswoman said: "A decision on whether someone is well enough to work is taken following a thorough face-to-face assessment and after consideration of all the supporting medical evidence from the claimant's GP or medical specialist.
"We encourage people to provide as much medical evidence as possible when they apply for Employment Support Allowance, and often people who are found fit for work only provide the necessary evidence when they ask for a reconsideration or an appeal.
"Since 2010 we have considerably improved the work capability assessment process, giving people a more tailored and personal service."
In a statement, Atos said: "Our trained doctors, nurses and physiotherapists strictly follow the guidelines given to them by the Government when conducting assessments and make no decisions on a person's eligibility for benefits."