Plans to replace the current system of welfare benefits with a single payment known as the Universal Credit will continue to "rot the soul" of the poor, Frank Field has warned.
The former Labour minister who advised the Conservative-Lib Dem coalition on welfare policy said that not only was work and pensions secretary Iain Duncan Smith's plan wrong in principle, it was also practically unachievable.
The Universal Credit will roll jobseeker's allowance, tax credits, income support, employment and support allowance and housing benefits into one.
But writing in The Guardian, Field said the government was wrong to argue the it would remove the disincentive to work.
"Means-testing only encourages dependency, and the universal credit is, in one sense, the ultimate form of means-testing," he said.
"It obviously gets extra money to hard-working families who earn low wages, but in doing so it rots the soul.
"Recipients have to be saints not to take the loss of credit payments into account when deciding whether to work longer or to train for a more highly paid job.
"At present, claimants can lose more than 90p for every extra pound in earnings. Under universal credit people can still lose about 65p of every extra, hard-earned pound – 20p more than the highest rate of tax."
In 2010 Field was recruited by David Cameron to conduct a review of poverty in the UK. However in 2012 the former welfare minister accused the prime minister of ignoring his findings.
Field also said today he did not believe the government was up to the job of designing a new IT system that would be able to administer the new system and warned of an impending "disaster".
The Labour MP also alleges that David Cameron shares his view and his attempt to shuffle IDS out of the DWP was part of a plan to ditch the changes to benefits. A move that was scuppered when his work and pensions secretary refused to budge.
The government has rejected the suggestion that the IT systems will not be ready in time and is due to come into operation in October 2013.