The research will reinforce ministers' determination to face down a growing Labour backbench rebellion over controversial plans to reform benefits to the sick and disabled, which soak up pounds 25bn of the pounds 100bn welfare budget.
According to today's Department of Social Security (DSS) statistics, almost 3 million people are on sickness benefits. They have become the largest single group amongst Britain's 6 million claimants.
In contrast, the number claiming unemployment benefit has fallen from 2.3 million to 1.3 million in the past three years, as the economy improved and the Labour government's "welfare to work" measures took effect.
Alistair Darling, the Secretary of State for Social Security, believes the new figures illustrate the danger that sickness benefits will replace the dole as the biggest problem facing the welfare system.
"We are not prepared to write people off at the age of 50 and to allow them to take sickness benefits as a form of early retirement," a government source said last night.
Labour claims that the previous Conservative government encouraged older workers to claim invalidity benefit - paid at a higher rate than the dole - in order to keep down the unemployment figures.
At least 60 Labour MPs are threatening to stage the biggest rebellion since the general election on Monday by opposing a shake-up of disability benefits when the Commons votes on the Welfare Reform Bill.
Yesterday 12 disability groups intensified the Government's problems by resigning from its Disability Benefits Forum in protest at what they called a pounds 750m cut in sickness benefits.
"The DSS has broken its promise that savings in disability benefits would come from getting people into work, not from restricting entitlements," said Richard Wood, co-chair of the Disability Benefits Consortium.
"It has ignored our constructive proposals during the consultation process," Mr Wood said.
Mr Darling will tell MPs on Monday that the reforms are not driven by a desire to save money, but because it is right to give those on sickness benefits the opportunity to do some work if they choose.