The Government's reform of incapacity benefits will "impoverish" a vast number of households and cause "untold distress", a new report has claimed.
A study found that the number of people on incapacity benefits will fall by almost a million by 2014, mainly among existing claimants who will lose their entitlement.
Researchers from Sheffield Hallam University said 600,000 people will be "pushed out" of the benefits system altogether, with the biggest impact being felt in Wales, Scotland and the north of England.
Merthyr Tydfil in Wales, Easington in County Durham, Liverpool and Glasgow look set to be hit 10 times harder than areas such as Kingston upon Thames in London or Wokingham in Berkshire, said the report.
Professor Steve Fothergill, co-author of the report, 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 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 under way 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."
Employment Minister Chris Grayling 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 re-testing 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. For those that need additional help our new Work Programme is up and running and will tailor support to people's needs so that they can overcome whatever barriers they face."