Half a million people who currently claim sickness benefits in UK are fit to start work immediately, a minister has suggested.

Employment Minister Chris Grayling gave the estimate as the coalition prepares to launch the biggest crackdown on abuses of the welfare system for a generation.

He said around five million people had consistently been on out-of-work benefits for the last decade.

“Too many people were left abandoned ‘on the sick’ while new jobs went to migrant workers from overseas,” he insisted.

He highlighted findings from pilot studies in Burnley and Aberdeen which showed “almost a third” of existing claimants were fit for work.

“The trial results show that, if replicated nationally, we could expect around half a million people to be found fit for work over the next three years as the reassessment exercise is completed,” Mr Grayling added.

Another 600,000 of the 1.6 million who will be tested are likely to be able to find work “with the right support”.

The welfare crackdown will see up to 10,000 people “reassessed” every week, with a process that can involve tough new medical tests.

Private companies will be used to help people off benefits and back into work, and rewarded with fees of up to £14,000 for each individual case.

Anybody ruled fit for work who is currently on an invalidity benefit will be placed on the less generous Job Seekers’ Allowance.

The coalition’s plan was first put forward by Mr Grayling when the Tories were in opposition more than three years ago. The then work and pensions secretary James Purnell came forward with similar proposals, but they are believed to have been blocked by Gordon Brown.