Most employment and support allowance claimants in Brighton and Hove who are turned down for benefits win their case on appeal.
Caroline Lucas, the Green MP for Brighton Pavilion, described the situation as a scandal.
She obtained figures from the Department for Work and Pensions (DWP) showing that 54 per cent of appeals from Brighton and Hove were successful compared with 37 per cent nationally.
The figures relate to appeals against fit for work decisions for new employment and support allowance claims between October 2008 and May 2012.
Dr Lucas said: “It’s a scandal that it’s harder to get help you’re legally entitled to in Brighton and Hove than elsewhere.
“I raised this issue with the DWP two years ago.
“They said they were improving the work capability assessment and that it would become ‘fairer and more effective’.
“Yet two years on, very high numbers of people in Brighton and Hove are still being wrongly assessed.
“People are still coming to me to express real anxiety about Atos and their poor assessments.
“Ministers know what’s going on but have been totally ineffective in sorting it out.
“In the meantime, people who are ill are still going through the worry and stress of having to appeal to get the help they need and to which they are legally entitled, possibly becoming more ill as a result.”