The government's tough new welfare reforms will force over half a million people off incapacity benefit and cause widespread poverty in some of Britain's most disadvantaged communities, according to a study releasedon Tuesday.

In the first independent attempt to quantify the impact of more stringent medical tests and the greater use of means testing, researchers from Sheffield Hallam University said Scotland, Wales and the north of England would suffer most from the changes to be introduced by 2014.

The study found that 600,000 people would disappear from the benefits system altogether and would often have to rely on family members for financial support.

Ministers have pledged to reform incapacity benefit after an almost fivefold increase to 2.4 million in the number of claimants since the late 1970s, and Chris Grayling, the employment minister, said: "It's clear that millions of people have been written off for years, left on incapacity benefit with no real support to get into work. That's why we are retesting people to see if they have the capacity to work. Our changes will make sure those in genuine need get more support and those who could and should be working are given the opportunity to do so."

But the co-author of the report, professor Steve Forthergill, said: "The large numbers that will be pushed off incapacity benefits over the next two to three years are entirely the result of changes in benefit rules – the introduction of a new tougher medical test and, in particular, the more widespread application of means-testing from next April onwards. The reduction does not mean that there is currently widespread fraud, or that the health problems and disabilities are anything less than real."

Fothergill added that the report's estimates on the impact of the reforms was based on experience in the pilot areas and on the Department for Work and Pensions' own assumption about the impact on benefit claimants.

The study found the reforms would have the greatest impact in areas that had been struggling for years to cope with job loss and where the prospects of former claimants finding work were weakest. Merthyr Tydfil, Easington in County Durham, Liverpool and Glasgow were likely to be hit 10 times harder than Kingston upon Thames in London or Wokingham in Berkshire.

Fothergill said: "The estimates show that the coalition government is presiding over a national welfare reform that will impact principally on individuals and communities outside its own political heartlands.

"In terms of the numbers affected and the scale and severity of the impact, the reforms to incapacity benefits that are underway are probably the most far-reaching changes to the benefits system for at least a generation. They will impoverish vast numbers of households and cause untold distress in countless more. The incapacity benefit numbers need to be brought down, but this is not the way."