Now that I've got a job in medicine where I don't have to wash my hands before I go to the toilet, it's easy to forget all that boring stuff about physical medicine. But patients who were banged up in the old-style psychiatric bins for their whole lives have 10 years shaved off their life expectancy and, apart from the fact that they all smoke about 80 fags a day, nobody can tell you why.

I'll tell you why. It's because the drugs are all dirty, and they've got junior psychiatrists like me, with all the postgraduate experience of a medical student, having to play at being GP for all their physical problems during weekends on call, and usually during the week too.

So I have a quick flirty moan with the girl from Saturday night as we hand over the bleep on a sunny Sunday morning (she's so fine) until I get called to go and look at two rashes on the ward. "Do you think it could be erythema purpuginosa?" asks the nurse. "That's why I called you."

I don't remember much about erythema purpuginosa. In fact, I'm pretty sure it doesn't even exist but smile anyway because in some hospitals when you're on ward cover and it's quiet, the single nurses will bleep you for trivia just to check out the junior doctor totty. And frankly, miles away from any big towns out here in the M4 corridor of London's party, I don't get many opportunities to meet girls my age.

Suddenly some bloke twice my size shoves a drug chart between my face and her breasts: "Sign here." I see Lorazepam 4mg scribbled on the front. Sounds like an awful lot of benzos to me. "She's kicking the shit out of Brendan and she's a drug-abusing personality disorder who never settles with less than 4mg."

We both look out of the nursing station window at a scuffle I have no desire or training to be a part of. But first-line management of aggressive behaviour is containment and seclusion, I suggest. "You're new, aren't you?" I smile because I can't think of anything else to do. "There are only four nurses on this ward today. Two of them are agency." I think he's being helpful.

They jab the assailant in the bum and she starts smiling because that nice warm benzo feeling is a great way to reward really aggressive behaviour, while I flick through the notes. This nasty piece of work with a personality disorder has been kicking the shit out of the same vulnerable 5-ft schizophrenic man twice a week for a month. If you're going to have that sort of thing going on then, frankly, there's no point in building your hospital in the first place. What's more, there is absolutely no reason why plenty of people with psychiatric diagnoses can't be responsible for their actions.

I flick through her notes and find an explicit entry from some eminent consultant. "In conclusion, it would be both appropriate and therapeutic that this woman should be held legally responsible for her actions. Particularly assault." My intuition is vindicated. I call the fuzz.

The boys in blue appear and manoeuvre around the ward, being uninterested but polite to everyone and showing no intention whatsoever of pursuing any charges. I suspect it may have something to do with a woman hitting a man, until I hear the phrase "pair of mentalists" and a bit of giggling.

I'm the first to say that professionals who work in difficult situations can be real human beings with real human responses, and you can't keep up a godly front all day every day. I'm not surprised if policemen dislike drug-takers or burglars more than Guardian readers do, what with all the abuse and beatings they get off them. But pas devant les enfants, darlings. And please don't just saunter off and leave this woman stomping around with her unboundaried sense of invulnerability. I prescribe a therapeutic arrest.

Of course, the fuzz tell the nurse they probably won't be pursuing the matter "but it's all on file", studiously avoid eye contact with me, and make for the door, when I feel a wave of self-righteousness gathering force inside me. I square up and put on my serious face.

"Look. She hit him and she's competent to face charges. Who's the psychiatrist and who's the policeman? You start assessing competence on the day I start spraying black people with CS gas."

That's what I'd like you to think I said. But you can't fight that kind of battle alone on a Sunday afternoon with a moderate hangover when you're just a little baby SHO psychiatrist, so I traipse back to the on-call room and watch the EastEnders omnibus on my own with a cup of tea.