In bed with Susan De Muth: Blood, tragedy, but the moon shines on: Peter Green

Dr Peter Green, 43, is a police surgeon in south London. His wife, Sally, is a doctor. They have two children: Greta, nine, and Piers, five.

Police surgeons are busiest between 11pm and 2am. It's when the alcohol boils over or people have been taking drugs at parties. I'm on call two nights a week to assess and record injuries at a variety of incidents. I don't usually bother going to bed - ours is a very busy patch.

Cases of child abuse are the ones that get to me. I've seen any number of children, eight or nine years old, who turn up by themselves at the police station in their pyjamas saying, 'I've just run away from home, Daddy's been beating me,' or whatever other hell they've been through.

It's particularly distressing because we have a five- year-old son, Piers, who is severely handicapped. You see these parents who beat the shit out of their lovely healthy children and you can't help thinking, 'Try having some of what I've got.' Kids get abandoned too - there was a two-year-old brought in a few nights ago.

I'm based at home and I actually quite like going out into the night. I'm reassured if I can see the moon: things in our lives get turned on their heads pretty rapidly but the moon still comes and goes every 28 days. Driving down empty streets you get a feeling of 'this is mine'. I finish at 6am when I'm on call. I might snatch a few hours' sleep then, but sometimes don't bother. Fortunately I can get by on relatively little sleep.

The cases I'm called to are very varied: assaults, incidents of domestic violence . . . even murder. My report will frequently be used as evidence in a court case. I am completely independent - not a police poodle. There have been cases when detainees have been injured by over-zealous police officers, against whom I have later given evidence.

I'm not upset by blood bespattered scenes. I simply get on with the intellectual work of collecting forensic evidence. However the human tragedies behind the drama, the catastrophic consequences of even relatively minor events on an individual's life, sometimes disturb me very much. Especially when they are too drunk or drugged to realise them at the time.

I sometimes find myself unable to stop thinking about people I've seen when I get home. Even if it is the middle of the night I want to talk things over with Sally; I go into the bedroom and make a bit of a noise in the hope that she'll wake up. She does get a bit annoyed, especially if she's been up with Piers.

Though I think a lot about my work it rarely crops up in my dreams. They are mostly symbolic, bizarre, surreal. If I understand them they can be enlightening. I once dreamt I had a cup of tea in one hand and a scalpel in the other. The image polarised the two sides of my nature - the comforting, pleasant me is the tea side, whereas a scalpel is dangerous and nasty and you stick it in. It's entered family jargon now: 'Well, that was a scalpel remark.'

Working from home certainly disrupts our family life. Even when I'm not actually on call, the Child Protection Team will often bring an abused child round to our house at night. It's unsettling, but at least we have the confidence of knowing that the child is getting a good, positive home atmosphere. We've had letters from children, with little drawings, saying, 'Thank you for being kind to me.'

We live according to a very strict timetable, sharing all responsibilities. Piers needs full-time care and a rigid routine. This virtually imprisons us but we have scheduled two evenings when we go out alone together - usually to feed our faces. Those evenings are essential - after Piers was diagnosed and we were told his prospects were unremittingly grim we both became intensely withdrawn and alone. We fell apart.

Sometimes Piers goes through stages of waking every hour through the night, screaming. It's better if we both get up to give him his bottle and change his nappy. If one sleeps through it, the other feels resentment. We try to support and comfort each other then. It's difficult not to feel bitter - Sally had an amniocentesis test when she was pregnant but our fellow medics somehow failed to pick up that the baby had a missing chromosome. You just think, 'Why me?'

Generally, however, my optimism has not been weakened by these experiences - rather it has been refined. I've learnt that to deal with any kind of disaster you have to look the devil in the eye. I like to think that I start each new day prepared, and brave enough, to face everything that comes my way.

(Photograph omitted)