Paedophiles and other sex offenders are to be prescribed Prozac in an attempt to prevent them reoffending, under radical plans approved by ministers.

The Independent on Sunday can today reveal that 100 prisoners in nine jails will take part in trials of the anti-depressant drug this autumn to test its use in suppressing obsessive sexual urges. An estimated 10 per cent of sex offenders could eventually be treated with the drug.

The Department of Health is also understood to be investigating the possible use of voluntary "chemical castration", which uses libido-suppressing drugs to treat sex offenders who do not respond to ordinary programmes.

The disclosure that ministers plan to use these controversial measures to deal with sex attackers comes amid a growing political row over how children should be protected from sex abusers.

The Metropolitan Police Commissioner, Sir Ian Blair, fears that removing sex offenders from bail hostels near schools will severely disrupt the offenders' treatment programmes and could place children at greater risk of harm, The Independent on Sunday has learnt.

The issue of how best to protect children from sex offenders has been thrust to the top of the political agenda by John Reid in recent announcements to tabloid newspapers.

The Home Secretary's announcement in last week's News of the World that he was also considering alerting parents to any paedophile neighbours drew accusations from senior police that he had succumbed to blackmail. Terry Grange, from the Association of Chief Police Officers (Acpo), said it was "policy-making on the hoof".

Britain's senior police officers are increasingly concerned about a shift in policy on how paedophiles are handled, which they believe could result in justice at the hands of the lynch mob.

Critics say the introduction to Britain of a so-called Megan's Law, based on US legislation under which names and addresses of paedophiles are publicised, would lull parents into a false sense of security and provoke mob violence.

Successful management of offenders is, say experts, the most cost-effective way to protect children. Drug treatment and the use of compulsory lie detectors for paedophiles on probation aim to further reduce the risk of reoffending.

Prozac - or its generic version, Fluoxetine - is already widely used in North America for the treatment of sex offenders, although it is effective only with the minority prone to obsessive thoughts.

Professor Don Grubin, who is leading the Department of Health-funded pilot, told the IoS that the drug could be effective in treating up to 10 per cent of offenders. "These drugs lessen their intensity and work on obsessive compulsive disorders. They also help with elevating mood."

Compulsory lie detector tests are seen as a useful way of preventing reoffending and breach of parole, but plans to make them mandatory have never made it on to the statute books.

Harry Fletcher, of the National Association of Probation Officers, said most sex offenders could be managed successfully.

"With the right programmes, sex offenders can be treated. There is no evidence that there has been any significant rise in attacks, and the number of kidnaps are so small they don't even record them."

How it works

Prozac stimulates the brain's production of the enzyme serotonin, which can cause loss of libido. The enzyme also boosts self-esteem and helps people overcome negative and obsessive emotions such as deviant desires to have sex with children.