Nearly a fifth of organisations that employ school staff say they have rejected at least one applicant in the past year because they are unhappy with their police records.

The TES can also reveal that the planned price rise for background checks by the Criminal Records Bureau means that teachers and other public-sector staff will effectively be subsidising the free checks for volunteer workers.

The Home Office announced this week that the cost of the full background check will rise from pound;29 to pound;33 in April. These checks are required for all new teachers and support staff.

As part of its attempts to justify the price increase, the bureau revealed research which showed that nearly 20 per cent of organisations in education had rejected an applicant because of details, not necessarily criminal convictions, on their police records. Vince Gaskell, chief executive of the bureau, said he had been alarmed that the level of rejections in education appeared as high as in other public services, such as care homes. Mr Gaskell said it was impossible to tell how many people the bureau had prevented from entering schools because it could not estimate its impact in deterring applications. The price rise comes only four months after the bureau raised the charge for a full disclosure from pound;12 to pound;29.

Mr Gaskell refused to apologise for the latest increase, saying that it was necessary to make the bureau, a public-private partnership between the Home Office and Capita, self-financing within two years.

He admitted that, under the new structure, teachers and other public-sector workers who pay for the checks will subsidise volunteers who receive free checks.

The price of a full check has risen to pound;33, despite the fact that the cost of producing it has dropped from pound;36 to around pound;30 thanks to improved efficiency.

Mr Gaskell said applicants needed to pay extra because the Government was halving its pound;18 million annual subsidy next year and the bureau had to cover the costs, estimated at more than pound;10 million a year, of carrying out free checks on volunteers.

The bureau is also considering introducing an extra charge for all organisations that register with it, including local authorities, teacher supply agencies, and hundreds of private schools.

David Hart, general secretary of the National Association of Head Teachers, said the service had improved since last year when some schools were forced to close temporarily because of delays with checks.

But he said the improvement did not justify price increases. “This adds insult to injury,” he said. “Schools have no option other than to obtain the checks which makes them a captive audience. The CRB has become a licence to print money.”