A contract killer named David delivers a sermon on prison bullying. He fashions a cosh by placing a battery inside a sock, and smashes it hard on the table. His audience, a group of visiting juvenile delinquents, is left in no doubt about its impact as an offensive weapon.
Watching on a television screen in the next room is George Martin, the 34-year-old inmate responsible for organising the tongue-lashing taking place next door. It is called the Inmate Experience Scheme, in which carefully selected criminals describe the harsh realities of life behind bars to young offenders.
After half an hour in front of the semi-circle of subdued-looking youths, David is replaced by Trevor, a biology teacher who murdered his wife; he said it was an accident; the court sentenced him to life imprisonment. Trevor talks movingly about the pain of separation from his baby daughter, and tries to describe what it is like to grow old behind bars. He holds up bedsheets stained with urine and semen, then passes a dirty chamber pot around the audience to illustrate some unappealing aspects of prison life.
'Basically we scare the shit out of them,' George Martin says. 'Young people should be educated about the realities of life as a criminal because it's not what they think it is. Kids see prison as being like the television programme Porridge. It's not like Ronnie Barker's experience. Prison is a degrading, humiliating, nasty, dangerous place to be.
'Apart from the physical conditions, people don't understand the mental side of prison life,' he says. 'Throughout my sentence I've cried myself to sleep. I even tried to commit suicide three times.
'Kids certainly don't realise the effect crime has on its victims. I never considered my victims,' he says. 'I say to kids, 'I know what it's like to be you.' I started offending when I was 13, and at that age you think you rule the world, and so wage war on society.'
George Martin is an expert in crime. But after 17 1/2 years spent in prison - his sentences the result of more than 250 convictions for theft, wounding, burglary and deception - he says he is determined to go straight. He was released from prison this week.
'I've been a professional criminal for all my adult life, and I saw imprisonment as an occupational hazard,' Martin says. 'I always considered myself to be a bit of a wide boy, and it wasn't until the beginning of my last sentence that I realised I wasn't - I was an idiot.
'I found myself in a strip cell, and began to wonder, is this how I'll spend the rest of my life, stuck in places like this? It made me determined to break the cycle and think that if I could persuade others what it's really like in prison, they would never get in the position I was in.' Then he saw a television documentary about a prison in the United States where young offenders were brought face to face with hardened criminals, and the idea of setting up his own scheme was born.
Martin has four children, but it is clear that being locked up on a regular basis has put considerable strain on his marriage. He was once invited by the headteacher of a girls' school in Liverpool to spend a day describing to the 750 pupils how marrying someone like him might affect them. 'My daughter was sitting in the audience,' he says. 'I asked her later if she was embarrassed by what I had done. She said no, she was proud that I was her dad.
'Kids are used to careers officers talking about getting a job, or to probation staff warning them that prison is a really bad place. But they've never heard anybody like me before. I tell them I've committed more offences than they could in a lifetime. I describe the drug-taking, rape, suicide and pissing in the pot that are part of everyday prison life.
'I never say to kids, 'Don't commit crime.' I can't say that because I did. What I do say is, 'It's your choice and your life. If you decide to do what I did, this is what's going to happen to you.' And I give them an informed choice.'
The youths at the session in the prison chaplaincy had just begun their criminal careers. Their offences were mostly shoplifting and stealing cars. All were detained in one of the region's secure units, and broken homes were a common feature. Some visibly wilted under the barrage. Others remained stony faced. Those foolish enough to smirk were verbally humiliated in front of their peers, who shrank back into their chairs, hoping to remain unnoticed.
When the group filed out three hours later, their earlier swagger and bravado had disappeared; the stale smell of sweat lingered in the room, a testimony to their anxiety.
As a result of his success with young offenders, George Martin has decided to join the crime- fighting business. When I met him in his cell-cum-office prior to his release, he immediately presented me with his business card. It describes him as a 'project officer' for Merseycare Trust, a branch of Liverpool's probation service. In prison, Martin was able to obtain private sponsorship of his pounds 12,000 wages and a pounds 5,000 travel and administration allowance.
Initially, many inmates and prison staff were sceptical about his ideas. Despite his criminal record, however, he convinced the governor that his version of short, sharp shock might work. The governor contacted the probation service, a year later Home Office approval was obtained, and the first session took place in February 1991. Now Martin enjoys celebrity status inside the prison.
The Inmate Encounter Scheme has since been expanded and will continue to be run by a small group of trusted inmates after his departure. Martin, however, has not turned his back on prison. 'He has written me a formal letter offering to come back to Garth as a paid consultant,' explains a rueful Roger Holding, the prison governor in charge of the scheme.
Once the youths are taken back to their detention centre, Mr Holding admits there is little to stop them reverting to their delinquent ways. 'Gut reaction tells you that this sort of scheme is the right approach, but it's difficult to know for certain because there's very little research to prove its success.'
George Martin disagrees. He brandishes handfuls of letters of thanks from young offenders. They claim to have been shocked out of their delinquent behaviour. Checks made with the probation service by inmates running the scheme suggest that one year after attending a session, 96 per cent of juveniles have not reoffended.
While the Home Secretary intends to spend pounds 75m building new detention centres for juvenile delinquents, George Martin is pointing out cheaper and more effective solutions. He is the first inmate to leave prison and take up a career as a crime prevention officer. The key to solving juvenile crime, he suggests, might be to use people like himself to educate children about the reality of crime. At present, he remains dependent on corporate charity for sponsorship and feels frustrated by the Government's blinkered approach towards juvenile delinquency.
'The Government may be intent on locking people up, but there are four convicts in Garth Prison who are determined to keep as many youngsters as possible out of prison.'