A crackdown affecting 24,000 Leeds Incapacity Benefit claimants will start within days.
Letters will go out to Incapacity Benefit claimants in the city from Monday telling them they are having their benefits reassessed and demanding they provide “full details” of their sickness or disabilities.
It warns them their “benefit may be affected” if they fail to return a questionnaire as soon as possible.
After returning the form, most will then undergo a Work Capability Assessment to determine whether they are fit enough to work or eligible to claim a replacement benefit, Employment Support Allowance.
Ministers are pressing ahead with introducing the tests, despite a stark warning from one of the architects of the new system.
Professor Paul Gregg, an economist and welfare reform expert, said: “The test is badly malfunctioning, The current assessment is a complete mess.”
During the preliminary roll-out of the test, people with terminal cancer and Parkinson’s disease have been found fit to work, and there were many more cracks in the testing and re-assessment system.
Around 900 claimants in Yorkshire will be tested each week once the scheme gets under way.
Latest figures show 24,650 people in Leeds are claiming IB, which is worth £91 a week to long-term recipients. There are 15,490 IB claimants in Wakefield and 14,170 in Kirklees.
Around 980 of the IB claimants in Leeds are aged between 18 and 24 - the sixth highest total in the country.
Employment Minister Chris Grayling said: “We will always help people who are sick and in genuine need by providing unconditional support, but we must ensure that those young people who have the potential to do something more with their lives are not simply shunted to the back of the queue as they were by the last Government.
“We will soon start assessing everyone on Incapacity Benefit to see if they can work, and from the summer our work programme will come on stream providing support built around the needs of the individual to help them on the journey to find a job,” he said.
Prof Gregg, who helped design the new ESA, has recommended a further trial before the tests are rolled out nationally.