Libby Purves: My son's teacher served time for sex offences, but I cannot condemn him

He was told that he must never even teach pensioners

I was haunted by two men last week. One is imaginary, a character in a novel I wrote. Another was my children's teacher when they were small. Both men could be classified as paedophiles. In current media rhetoric that should damn them beyond redemption, even of the divine variety - on Radio 4's Sunday programme Christian and Jewish speakers both opined that such monsters should be discouraged from coming to church.

The teacher first. Nicky was a cheerful, boyish figure; he once ran a cycling camp in our field. In 1997 he got a three-year sentence: Dunblane and Marc Dutroux had dominated the news for months, which may account for its severity. His offences were slight: there was one small complaint of touching, followed by widespread police trawling and questioning of baffled children. Crucially, his computer was examined. He had not been downloading porn, but wrote a private diary of his feelings towards boys. That condemned him. The court refused to allow the many positive character references, including one from my 12-year-old son.

I visited Nicky in prison over 18 months on the principle that if he came out friendless he would be far more at risk of offending. He was an exemplary prisoner, spent long periods with the chaplain, and once said: "Don't worry, I know what's what. Perhaps I should never have been a teacher." I drove him home on Christmas Eve; he was banned from church on Christmas morning but later found a better one, lived with dignity for a couple of years and then died of a heart attack.

It was Ash Wednesday. Earlier that day he told his priest that he kept the ash of repentance on his forehead all day, and was proud when people stared. His greatest grief was losing his work: he had hatched a plan to teach immigrant women English but was told that this was barred and he must never even teach pensioners. Ironic, given last week's revelations.

Around that time, too, a local choirmaster (against whom no evidence ever emerged) committed suicide after police questioning. Men often do. It struck me that there was a problem here: what do you do if you have never offended but fear that you might? Where do you go?

I researched it. There was virtually no confidential help, especially for a teacher. Yet teaching might well be the one way to sublimate those feelings, loving children safely, twisting awful desire into kindness. Psychiatrists refer to paedophile yearnings in teachers as a "déformation professionelle", but even psychiatrists know that temptation can be resisted.

It must be lonely living in a sexually lax society while afflicted with the only orientation that you can't have pride marches about. Easy to see the lure of websites: perhaps for nasty gratification, but perhaps also just as an attempt to understand, to learn how to manage yourself. It is a complex issue, not a simple one.

The theme of the inactive paedophile wrestling with his desires became so pressing that I built a novel round it. More Lives Than One, published in 1998, has a teacher hero called Kit Milcourt.

I never gave away its theme on the cover because the point was to get the reader on his side, liking him, amused by him. Only on page 183 would they get the shock of knowing what he battles with. So there was a double-twist: on a school trip to Venice he is wrongly accused of kissing a girl of 12. She eventually recants her lie, but the investigation and suspension make Kit crack. Late one night he admits to his wife: "It wouldn't have been a girl..." and says what he is. "A fixated preferential paedophile, and not even a sensible one. Sensible ones jump off high buildings or drive into trees as soon as they understand what they are." He has never touched a child and hopes he never will, but her shock and disgust - and his desire for death - overshadow the rest of the story.

The response from readers was fascinating: shock, sometimes reproof ("I thought you were such a warm writer"). But just occasionally a hand reached out across the gulf: a man murmuring 'Yes, that's me"; a wife whispering "I married one, I keep him safe." I am not naive: one or two letters were from the most disgusting, self-exonerating kind of guilty paedophile. But most were not. Many were teachers. The tone was of fear. "Not fear of discovery, I've done nothing, not even websites. Fear of myself."

CS Lewis said that the easiest sins to condemn are the ones that do not tempt you. Since few of us want to interfere with children, we rant freely against those who do, even if their offences are slight, regretted and unlikely to recur. Perhaps we are also assuaging our vague general guilt at tolerating imagery and culture that sexualises children - marketing thongs and bikinis and Britney to seven-year-olds.

So we oversimplify and swallow wholesale the glib mantra that they are all devious monsters and that by the time a man is accused of anything he has probably been at it for years. We never ask the most important question: how we can help the inactive, the tempted, the tormented, the innocent? How can we keep them safe? I have no answer. I just wish we would ask the damn question.

'More Lives Than One' by Libby Purves is published by Hodder, £6.99