Severe delays on checks by the Criminal Records Bureau are driving thousands of nurses, teachers and social workers to leave their professions. About 5,600 people have been waiting up to seven months to start work in children's homes, hospitals and probation services, according to the latest figures.

The bureau, beset by problems since it was established in March, is struggling with a backlog of 89,000 applications from its total of 216,000. It faces a shortfall of about 9,000 out of the 40,000 applications it receives each week. The average waiting time is now six weeks, with only 50 per cent of applications processed within the target three-week timescale.

Harry Fletcher, the assistant general secretary of the National Association of Probation Officers, said that the rate of departure for frustrated care professionals could leave nursery, probation and social services crippled. "Many of the thousands who have been waiting for months will just give up and leave. They cannot live on air or benefits indefinitely."

A Home Office spokesman admitted the backlog "may be rising slightly" due to increasing uptake by organisations such as Scouts, nanny agencies and voluntary bodies.