Agency doctors are up to £4,500 a year cheaper than locums from the NHS's own staffing bank, claims new research.

Independent analysts Laing and Buisson compared the cost of employing doctors through commercial agencies with NHS Professionals, the in-house agency used by more than 60 health trusts.

It found a locum from NHS Professionals' bank of doctors costs on average£2.40 an hour more than one employed by a medical recruitment agency signed up to the national framework agreement.

This works out about£4,500 a year more. But the report suggests the cost difference could spiral to£10,000 should NHS Professionals increase charges to tackle debts.

The report also found commercial agencies had much higher success rates for filling doctor vacancies and shifts. On average they scored a 61 per cent 'fill rate' in 2006-07 while NHS Professionals achieved just 35 per cent.

The findings challenge common perceptions about agency doctors, said the Association of Medical Recruitment Agencies, which commissioned the research.

The association also claimed its workforce undergoes more rigorous screening under regulation by the NHS Purchasing and Supply Agency - staff are subject to yearly criminal record checks and must meet '100 per cent' of a long list of quality standards, said AMRA executive committee member Kate Bleasdale.

She said the NHS tended to 'pick and choose the standards they think are important'. 'People assume agency staff are lower quality and higher cost and this report very clearly refutes that,' she added.

An NHS Professionals spokesman denied its staff had less stringent checks, and added that locum doctors only represented£10m of NHS Professional's£235m turnover.

'In terms of prices quoted, they reflect the discounts trusts working through NHS Professionals and the NHS Purchasing and Supply agency can enjoy,' he said. 'These prices are typically not realised by trusts not using NHS Professionals.

'We accept this small part of the business is loss-making. However, this is not a structural issue and we have brought in a new management team to turn the business around.'