A report out today recommends a review of the prevalence of mental health problems among offenders after revealing that only half who would benefit from treatment are sent to secure hospitals.
The report, commissioned by Laing and Buisson, said the cost to the taxpayer of mishandling offenders with mental illness was more than £600,000 per prisoner.
It said the 1.5% of the prison population who had a severe mental illness would benefit from admission to hospital. But many were not transferred because commissioners failed to account for hospitals provided by the private sector.
Of the 3,200 people the study estimated would benefit from hospital treatment, only 1,458 were transferred into a hospital setting in 2007.
The study found that the most violent offenders would benefit most from hospital treatment. Their reoffending rates dropped by up to 58% when compared with those who had not received treatment.
The lifetime cost of high-risk prisoners who re-offended was estimated at £663,570, with the net cost of treatment totalling £36,630. The total saving from treatment was £626,940.
The costs were based on offenders having an 18-month stay in a secure hospital which, the report said, was more effective in reducing offending than shorter periods of treatment.
Report author Dr Judy Renshaw said: “Staff should recognise that there are alternatives for people with very severe need and they should be considering it in the decision-making.”
Renshaw’s report is due to be presented to ministers at the House of Commons today.