'I can give up crime, doc, anyone can do that - but how can I stop behaving violently? It's the only thing I know!' Michael puts his head in his hands, 'I'm going to hit someone soon, I know it, and then I'll be finished'.

Michael is part of that extraordinary community that happens to be prison; that group of people whom society has decided should be locked up. Most but not all are young, some are powerful and dangerous, some so inadequate that they can scarcely survive and quickly become underdogs. Most are caught up in the drugs business, without which the prison would be virtually empty. Some have killed the only person with whom they could not live and are now harmless; some are like the grey haired smiling Irishman who clapped his hand on my shoulder, laughing, 'They say crime doesn't pay, doc - don't believe a word of it!' They are the professionals. On the surface the prison is run by the 'custody officers', but underneath powerful gang leaders dominate and terrorise the weak. All of them make up your practice if you decide to become a prison doctor.

An average day

My morning starts at the prison gate; a huge cliff of red brick, imposing and intimidating. The massive royal coat of arms looms over me as I enter. Getting in is tedious and time consuming. I take out my credit card ID with the convict picture labelled 'prison doctor'.

'Hi doc', shouts the duty officer on the gate from behind a bullet-proof window. His voice comes muted through the sound system. 'You're wanted at Seg', he adds. 'Seg' is invariably my first port of call. It is the segregation unit, the punishment block for prisoners who have offended in some way; been rude to a member of staff, found with drugs, or guilty of violent behaviour. I stand patiently while the automatic doors close behind me. A lengthy pause and then the doors at the other end start to open. Once through I claim my enormous bunch of keys.

I walk into the yard, surrounded by more acres of red brick topped by barbed wire. Men in grey overalls wave to me: 'Hi doc, did you get my X-ray result?' I arrive at the segregation unit. Every inmate there has access to a doctor daily. They have individual cells and the deprivation that seems to be most serious is that they have no television. They are unable to work and get little opportunity for exercise. A member of staff shows me round. There is the usual run of complaints: 'How come I didn't get my medication, doc?', or, 'I didn't get my appointment'. Many are still asleep, even though it is well past 10am. I often think that I could do with a fortnight here to have a rest and catch up with my emails.

I go on from here to the health block, where morning surgery is about to begin. The prison service invests hugely in the health of its guests - there is a staff of perhaps 25, with specialist prison nurses, community psychiatric nurses and visiting staff of all kinds. Some will be committed to prison work and revel in the challenges and opportunities it presents; others will be indifferent. Many will not be around long, contributing to the high turnover of health staff in prisons. The professional isolation, frustration and mediocre pay all militate against continuity and happiness at work. There are two part time GPs making up one whole time equivalent as well as visiting psychiatrists.

We have tried to get consultants from our regional hospital to visit but they felt that it was a 'poor use of their time' and as a result many prisoners need to visit outpatient departments. This is a huge problem as the prison needs to send two or even three custody staff with them. In spite of the indignity of being seen in public chained to prison officers, many prisoners are only too glad to get into the outside world for a few hours. The administration hates the huge costs and manpower involved; prisoners are often adept and sophisticated at feigning disease. As a prison doctor you are in the middle.

Tricks of the trade

Consultations are long and I often wonder what we are doing. Many men have suffered abuse as children and young adults; many, like Michael, know no way of getting what they want other than by manipulation or aggression. A GP learns quickly how to defuse violent situations, but if not there are plenty of staff on hand and I feel safer than in a normal surgery. The surprising is always just round the corner: one suggestion of a rectal exam produced a sudden explosion of, 'I've had enough of that' and the patient stormed out, leaving me to guess at the unfathomable depth of his childhood abuse and the rape he might have endured then or within the prison. At the other end of the spectrum are the frequent requests for letters: a note that will unwind the prison bureaucracy and get your patient a new mattress, or persuade the staff to allow a non-smoker to share a cell with someone who does not smoke 40 a day.

The amount of purely physical pathology I see is amazing and exceeds that found in general practice. As for psychiatry, it is all there in every shape and form. Drug addiction is rife and the prisoner who does not admit to having been involved in drugs is rare indeed. Prisoners often continue their habit while at Her Majesty's pleasure and in spite of the sniffer dogs the prison is overrun with drugs. The visiting arrangements make it possible to pass drugs and other items from hand to hand or from mouth to mouth and in spite of the fiercest sanctions that are regularly applied it happens all the time. Various liquors are manufactured and sold on site. This is all in spite of strenuous efforts by the security staff. Many prisoners are extremely clever and wartime prison camp stories are re-enacted daily.

There is a growing substance abuse treatment scheme, but its early efforts were severely compromised by a replacement programme using buprenorphine. Huge numbers signed up, including some of the very few people who had no experience with drugs. The preparation was effectively distributed around the prison and a flourishing market for it established.

'You came to visit me'

After the clinic comes visits to the blocks where the prisoners live. These visits are often not strictly necessary but are vital if the doctor is to see the living conditions of his patients. Cells at my own prison are tiny, but are individual and have a basin and toilet. Some cells are festooned with pictures of family, others with pornography. In some the atmosphere is thick with cigarette smoke, in others with the aroma of cannabis. The TV is invariably on. The noise level is inhuman. I am always welcomed cordially, as if to someone's home, and in a way it is a privilege to be there.

Afternoon clinic starts at 2 pm and by 5 pm I am emotionally and physically exhausted. If you are thinking of becoming a prison GP, then it is advisable to be part time. Three days a week in prison can be a great experience but can leave you wondering if everyone in the world has five hidden and not so hidden agendas. A full time job can make you lose touch with life in the 'normal' world and with normal medicine.

It is perfectly possible in most prisons to be a psychiatrist, or other specialist who visits on an occasional basis, but it is the GP who makes such a difference to the lives of prisoners. The prison doctor's relationship with the prisoners is special; akin to that of the chaplaincy staff. The doctor is one of the prisoners' advocates, and is emphatically not one of the custodial staff. However, the prisoners will quickly find out the attitude of their doctor. This is the tightrope walk; to be their advocate and friend without ever colluding in their behaviour or taking their situation lightly.

'I was in prison and you came to visit me' (Mt 25:36). The Son of Man, in his heavenly glory, with all his angels around him, is dividing the sheep and the goats, and what concerns him most? That we should have noticed and looked after those with whom he so closely identifies. We need not take this literally...but we can! God cares deeply for those who have been locked up by society. On what basis does Jesus intercede for us? Not on that of our innocence but of our guilt! We are all guilty. As a Christian I relate to these people not on the basis that I am better than they are but on the basis that I am also guilty. I am acutely aware that there is only one difference between them and myself - my sins are secret and socially acceptable, whilst theirs are not. I have been blessed to be born into a home where I was loved.

Michael is one of those precious people whose sins are far from secret - they destroy his own life and that of others, but they have been forgiven, and he has started that supremely difficult road to rehabilitation and a relationship with Christ. Some are able to write books about how they found Christ in prison. For most the reality is very different and unspeakably harder. Prison is a harsh environment for a Christian to grow in, full of pitfalls, temptations and mockery, but the greatest difficulties are within: the illiteracy, the lack of love, the deeply ingrained destructive habits. It is these people that I as a doctor have the privilege of standing beside. I can make an appointment to see them any time. They don't have to come, but they probably will. You can see them alone, you can pray with them. You can be a lifeline in your position as 'neutral'.

Michael shows me his poems; reams of them, some simple and adoring love poems to his Saviour, many speaking in simple and desperate terms of his struggle to live a new life. On the drive home I pray loudly for him. I tell God that if he is not going to be Michael's God then I am not interested in him being mine. But Michael is hanging in there. He is 'going on with Christ'. God is being Michael's God.