BBC's Jane Peel outlines the dilemma facing authorities

The inquiry suggests prison sentences that would prevent the offender being released - until it is thought to be safe.

The release of paedophiles Robert Oliver and Sidney Cooke last year prompted public disorder and protest.

It highlighted the problem posed by dangerous offenders who are not suffering from a treatable disease, yet still pose a threat to the public.

Sydney Cooke: Authorities are still unsure what to do with sex offender

Dr Peter Snowden of the Royal College of Psychiatrists says it is a great difficulty for his profession.

He believes they are asked to look after such people "without any research evidence that proves the treatment is effective".

There are two options in such cases. Offenders can be sent for treatment at a psychiatric hospital or secure unit, but this is only allowed if two doctors agree on a diagnosis.

Prison is the alternative, although the offender must eventually be released into the community if a life sentence was not initially handed down, leaving the public still at risk.

Peter Fallon's report into Ashworth recommends jail rather than secure hospitals, but wants each case to be reviewed at the end of the sentence.

"If they are still a risk," he says, "they should be kept in".

The reviewable sentence idea has government support, and is backed by many in the probation system.