For most of the 20 years he spent in prison, Tony had used drugs every day: heroin, cocaine, amphetamines, anything he could get his hands on. Two years ago, when he woke up in the strip cells in Ford Open Prison, West Sussex, after a three-day binge, he decided it was time to quit. He was granted a transfer to HM Prison Downview, in Sutton, Surrey, home to the Addictive Diseases Trust (ADT), a ground- breaking charity that had just set up the only full-time drug rehabilitation programme inside a British prison.

It proved a revolutionary decision; not only was Tony drug-free within weeks, but he also went on to become one of two full-time 'peer counsellors' working for the trust within the prison.

Most of the work is undertaken by trained counsellors with histories of addiction. Many, like Tony, are former prisoners. Employing former users and convicts in a drugs project is controversial, but Peter Bond, ADT's training and development director, defends the policy: 'Most programmes are designed by people with no experience of addiction. We can see where these people are coming from.'

Mr Bond is a former navy captain who lost his house, business and family through drinking. He sobered up with the help of Alcoholics Anonymous and now strongly advocates AA's methods: 'The programme gave me my life back.'

The prison's 'therapeutic community' uses temporary accommodation in the prison grounds, known by inmates as the 'serenity shack'. Tony serves as the first point of contact for inmates: 'I tell them what ADT has got to offer, and they can come if they want to. They can identify with me as a serving con. Some of them know me from jail - they've seen me stoned out of my nut, and they think, well, if he can do it, so can I'

Tony, who is serving a life sentence for murder, has enjoyed a dramatic transformation. He had been using drugs from the age of 14, and shot his partner in the course of a robbery when he 'was out of his mind' on cocaine and alcohol. Prison did not cure him of his bad habits: 'Thanks to my drug use, I was completely psychotic. There was no way they could have let me out - I'd have killed someone else. I'd have been back inside in days,' he says.

The centre has used prisoners as counsellors since its opening in April 1992, and Mr Bond hopes that eventually 60 per cent of counsellors will be drawn from the ranks of inmates. The idea was born six years ago when Mr Bond, by then recovered, went to a seminar run by Joe McQuaney, an American who travels the world preaching the AA gospel. Impressed that a black man should have managed to sober up in Arkansas during the Sixties, when segregation was routine, he went to stay with McQuaney in Little Rock. There he visited three prisons where McQuaney ran drug-treatment programmes modelled on AA methods. Theywere successful: re-offending rates had fallen from 60 per cent to 25 per cent.

Mr Bond returned to Britain, met Jonathon Wallace, a journalist and recovering alcoholic who was counselling other addicts. He told him of the American prison work.

This was just the kind of project Mr Wallace had been searching for. 'I'm reluctant to use the phrase 'divine guidance', but it was remarkable the way everything fell into place,' he says.

In 1991, the two men registered ADT as a charity and set out to find a prison willing to offer them a chance to launch their programme. They made informal approaches to more than 20 prisons and then approached Downview. 'We knew the governor would have to be willing to risk his professional life by taking us on board,' Mr Wallace says. Derek Aram, then governor of Downview prison (now with the directorate of health care, HM Prison Service), took the risk. 'Appearing when it did, ADT was a godsend, because it filled a gaping hole in our ability to tackle serious substance abuse in prison,' he says.

David Lancaster, the new governor, was happy for it to continue: 'It is a beacon lighting up the darkness. It offers a way through to recovery,' he says.

ADT aims to put between 80 and 100 prisoners a year through its intensive, 72-day programme of group therapy, one-to-one counselling, lectures and written work. Its graduates have access to free after-care at any of the numerous AA and Narcotics Anonymous meetings that take place around the country.

It is too early to produce statistics, but the anecdotal evidence is good. Word has spread and other prisons are planning to set up similar programmes. ADT has been inundated with applications for transfers from prisoners around the country. Two other prisons and a juvenile detention centre also want to set up treatment programmes. Whether or not the funding will be forthcoming from the Home Office may depend on a report on its work by Judge Stephen Tumim, HM 5Chief Inspector of Prisons, due to be published shortly.

ADT estimates that if it can 'help one man to help himself' and avoid a four-year sentence in prison, the saving in police, judicial and prison costs will total pounds 100,000. The cost of running a treatment centre for a year is estimated at pounds 120,000.

Mr Bond claims that more than 50 per cent of inmates have 'chronic' addiction problems. Some develop a habit while in prison; others are led into crime in the first place in the search for money to feed their addiction.

Mr Bond says: 'This treatment is about learning to cope with life - I used to drink because I was very shy and retiring, but it didn't help. I have some dignity now, and some self-respect.'

Tony is keen to put something back into the programme, and works hard in the prison community. Yet he realises ADT still has much to offer him as well: 'I'm not doing this for anyone else - I'm doing it for me. I've got peace and serenity in my life now, and working here means I've got a better chance of staying clean,' he says.

(Photograph omitted)