Britain is to examine why so many people end up on long-term sick leave, fuelling a 192 billion pound annual bill for welfare, Prime Minister David Cameron announced on Thursday.

The government is already preparing to reassess the circumstances of 1.5 million people off work on long-term incapacity benefits to see if they are fit enough to return to employment.

But it also wants to reduce the flow of new claimants, Cameron said at an event to mark the publication of legislation to overhaul Britain's benefits system.

Half the people who end up on Employment and Support Allowance each year start by being signed off sick from work, Cameron said.

The review of sickness absence will recommend what can be done to end the sick-note culture and improve health and wellbeing at work, Cameron said.

We simply have to get to grips with the sick-note culture that means a short spell of sickness absence can far too easily become a gradual slide to a life of long-term benefit dependency.

The review will be conducted by Carol Black, the government's national director for health and work and David Frost, the head of the British Chambers of Commerce lobby group.

The government's plans to reform welfare promise more help to those out of work but threaten sanctions against those who avoid getting a job.

The changes are politically risky and could provoke a public backlash, coming at a time of rising unemployment, state spending cuts and an economy weakened after a deep recession.

The government hopes simplifying a web of different benefits into a single universal credit will wean families off state dependency.

The reforms will initially cost more money but in the long run aim to save 500 million pounds a year in administrative costs.

The government separately plans to cut a range of benefit entitlements to save a further 18 billion pounds annually.