A survey of prisoners at Grendon jail in Aylesbury, Buckinghamshire, found only a third of 214 men who went through its programme were reconvicted within two years of release, compared with up to nearly a half of those held in the other 130 jails in England and Wales.
In his report, following a short, unannounced inspection at the jail in May, he concludes there is 'cautious reason for optimism' that the therapeutic regime - which includes individual and group work with psychologists and psychiatrists - is working.
The report says: 'The therapy programme appeared to be successful in improving sensitivity and social skills.'
But it warns: 'There was less evidence that deep-rooted personality and behavioural difficulties were being addressed as effectively as they might be.'
A medium-security prison, Grendon holds about 180 inmates - including 66 lifers - mostly serving sentences for sex and violent crimes.
But what makes it exceptional is that prisoners have to volunteer to serve their sentences there, agree to take part in all the programmes, and agree to assessment before they are selected.Reuse content