Censorship is easy to ridicule. No job is as absurd as that of the person who earns a living snipping the willies out of
Raunchy Cowboys III. Many of us - having accidentally tuned in to the hotel adult movie in our conference bedrooms late at night - wonder at the care taken to excise the ruder details. Lascivious downward pans end inexplicably at the navel, jump cuts plunge the viewer from busty foreplay straight into strenuous coitus - presumably because this is the one circumstance in a porno pic in which the genitals are, mmm, covered. The effect is disconcerting, like walking fully clothed through the door of a swimming pool and into the water; the mind simultaneously absorbing both the intention of the pornographer and the strategy of the censor.

Censorship is easy to ridicule. No job is as absurd as that of the person who earns a living snipping the willies out of Raunchy Cowboys III. Many of us - having accidentally tuned in to the hotel adult movie in our conference bedrooms late at night - wonder at the care taken to excise the ruder details. Lascivious downward pans end inexplicably at the navel, jump cuts plunge the viewer from busty foreplay straight into strenuous coitus - presumably because this is the one circumstance in a porno pic in which the genitals are, mmm, covered. The effect is disconcerting, like walking fully clothed through the door of a swimming pool and into the water; the mind simultaneously absorbing both the intention of the pornographer and the strategy of the censor.

The nation's chief censor, chairman of the British Board of Film Classification, is - of course - our own Andreas Whittam Smith, who, the day before yesterday, invited readers to comment on the latest court case involving his board. As he reminded us (and as I cannot resist repeating), the videos at the heart of the judgment included Nympho Nurse Nancy, Horny Catbabe and Office Tart.

For some time now, even videos sold at licensed sex shops, depicting what you might call "straightforward sex" (violent sex and sex involving children or animals being banned by law), have been subject to restrictions. As Andreas put it, "Erections may be shown, but there must be no clear sight of penetration or of masturbation or of ejaculation." So adults have not been able to purchase films showing sexual activities that rank among the most common available.

Then the manufacturers of Catbabes and Horny Tarts, as was their right, appealed against the ruling of the board. The Video Appeals Committee of the BBFC, by a narrow majority (including two women novelists), overruled the board's decision. The board took the case to court and lost. Mr Justice Hooper ruled that the appeals committee had struck the right balance between freedom of expression, on the one hand, and the possible harm that might be done to children, on the other.

The board's counsel had argued that, since so many children had access to video players, there was a danger that some of them would get to see the masturbating nurses and penetrated cat-tarts, and - as a result - be damaged. More damaged, in fact, than they would have been by witnessing an erection or two. The appeal committee's brief, for his part, contended that certification could be refused only if "it was shown that there is devastating damage to a significant proportion of children", and went on to argue that such a case had not been made. The judge agreed.

It seems to me that there are three issues here. First, is it the case that more children will actually see more frenzied ejaculations as a result of this ruling? Second, if they do, will they be harmed in any way? And third, even if the answer to the first two questions were to be "yes", would prohibition be the most effective method of dealing with the problem?

The third law of parenthood is that you must assume that children will find everything, from attractive-looking pills to their Christmas presents. If the videos are sold, some children will discover them where they have been secreted in cupboards, desk drawers or under beds, and will watch them, and show them to their friends. In the pre-video age we sneaked into horror movies, or exchanged books with nudes in them. It hasn't changed.

So what about damage? "Visceral clutch" (I can't remember who invented the term), perfectly describes my own reaction to the possibility of my children being shown movies full of masturbation and ejaculation. Were I to find out that one of them had been to Jonny's place and watched a mucky movie, that would be the last time they would set foot in that house. I cannot think of a responsible parent who would willingly allow their child to be exposed to hard-core pornography.

Ah yes, but is that restrictive impulse justified? Would such exposure really (asks the siren voice of ultra-liberalism) be so bad? Am I attempting to realise an ideal of childish innocence, a construct at odds with the facts? Isn't the truth that I am frightened by my own children's sexuality? After all, there is no extant research that shows that children are harmed by seeing sexually explicit images. And didn't, for many years, working class and peasant children grow up in shared bedrooms where adult sexuality could hardly be kept a secret? Such children may possibly have been enlightened by witnessing an act that is pretty universal. Chill out.

If you've been nodding along to all that, then I have a shock for you. All the above is more or less what paedophiles argue. They need to believe that children are not damaged by non-enforced sexual encounters, and that such encounters constitute a form of teaching. The modus operandi of many paedophiles involves the exposure of their targets to pornography, presumably because this "normalises" adult genital sex for the child.

But there's no proof. One of the things that drives me crazy about some anti-censorship liberals (as a liberal myself) is that they refuse to accept the cost of their liberalism. For years they have been trying to convince us that you can churn out increasingly attractive violence on screen, but never in any way add to the amount of violence in society. This completely counter-intuitive proposition (one which no ad agency would credit for five seconds) is bolstered by the lack of hard evidence that those who watch violent movies go on to offend themselves.

Yet, what you can say, as Professor Kevin Browne of Birmingham University has discovered, is that those youngsters predisposed towards violence, are stimulated by screen mayhem. So it isn't too far fetched to suggest that films indicating the normality of certain kinds of sexual encounters, are likely to "permit" some children to emulate them. If so, then that's damaging enough, because we certainly do have research which indicates that early sex results in increased incidence of STDs, teen pregnancies, low self-esteem and unsatisfactory sexual encounters.

Even if you are not inclined to accept this chain, you might agree that we should invoke the famous precautionary principle - that "devastating damage to a significant proportion of children" is far too high a threshold. At the moment I am not at liberty, for instance, to plant my garden with GM oil-seed rape, for fear of contaminating my neighbour's garden. But I am (as of now) allowed to decorate my internal garden with oil, seed and rape. And the risk to my neighbour is thought too negligible for the state to demand that I stop.

So, yes and yes and on, briefly, to the third question. It is hardly likely that a government that issues advice on the inherent dangers of musical chairs is going to sit by and allow sticky videos to be sold openly. Soon Mr Straw will emerge clutching a Bill aimed at preventing an avalanche of filth from engulfing us. But, like GM seeds, the problem is that this stuff is already out there and widely tolerated. On the Net you can indulge any perversion you like providing (a) you can pay the phone bill, and (b) you know what it's called. There are ways of screening out the most obvious dangers, but they can all be got round with a little ingenuity - ingenuity that can be shared in the playground.

Which leaves us with the only defence that really works: good parents. Which is another story.

David.Aaronovitch@binternet.com