The idea that giant institutions are efficient is a primitive superstition that daily experience disproves, so is just the kind of thing that British governments are inclined to believe.

I do not often agree with the Prison Reform Trust, but on the proposed construction of giant prisons - the criminal justice system's answer to giant casinos, I suppose - I do wholeheartedly.

The dangers of gigantism in prison are very great. Running a prison without resort to brutality requires a delicate balancing act. The necessary co-operation of prisoners cannot be obtained by brute force alone, but staff need to maintain the upper hand. As every prisoner knows, most brutality in prison comes from prisoners, not staff. When the staff lose control, brutality increases.

I've seen this for myself in extreme form when I visited Lurigancho prison in Lima, Peru, years ago. It had 7,000 inmates. I visited the comparatively salubrious part, el jardín, the garden, so-called because there was a tree somewhere in it. Brutal as it was, it was like a garden party compared with the part reserved for the worst prisoners, where the staff never ventured. I observed it from a roof, and within a few minutes saw one prisoner try to kill another with a huge shark hook. Food was thrown over the wall to the prisoners.

No doubt it has improved greatly since then, but huge numbers are not easy to control, even with the best will (and technology) in the world. La Santé in Paris, the largest prison in France, is notorious for its brutality, much worse by all accounts than anything in Britain; and although the Government will claim that it will never cut corners to produce the same conditions in Britain, who will believe it? The temptation to park large numbers of prisoners together and leave them to get on with it will be great, especially in times of economic stringency. And most times are times of economic stringency.

Of course, some might think that more unpleasantness is just what prisoners need, that our prisons are much too soft. This is a perennial complaint: I remember more than a third of a century ago, when conditions were much harder than now, joining a magistrates' tour of a prison, in the course which one magistrate extolled the disgusting food with the words that he wouldn't mind moving in and living off it himself. I was impressed neither by his honesty nor his humanity.

The main purpose of prison is to keep wrongdoers off the streets for as long as necessary, which is usually much longer than our courts acknowledge. It is not to brutalise or humiliate prisoners, which vast and impersonal prisons are more likely to do. Huge prisons do not make us modern, any more than model rockets made Zambia a space power.

The author is a former prison doctor

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