This week The Independent has revealed a lot about young Britain, not least about its attitudes to sex. It should be meaningful, they say, or forget it. Did you say forget it? asks Glenda Cooper

"It doesn't matter how liberal you are, because by the time we are in our twenties we are fed up with meaningless sex." Damian Julienne, 19, from Birkenhead, told the 2020 Vision survey - the biggest ever conducted of young people - yesterday.

Oh really?

What are we to make of the youth of today? That they'd rather be sitting quietly at home revising for exams, in a stable relationship, and saving for their pension rather than attending drug-crazed orgies and being gratuitously rude to their parents? So they say.

"Huh, these ungrateful teenagers. Meaningless sex? Chance would be a fine thing," snorted one colleague yesterday. It seems that today's youth are more responsible than their forebears. They - and I - blame it on their extensive sex education, which tells them all they need to know about sex so early in life that they end up agreeing not with the late poet laureate John Betjeman (who said his only regret was that he hadn't had more sex ) but with the fourth earl of Chesterfield, who thought that "the pleasure is momentary, the position ridiculous and the expense damnable".

Actually that's a bit unfair on Damian and pals who do not condemn sex per se. ("My friend's got three kids and he's got another on the way. But since he turned 17, he's settled down with his girlfriend. I suppose that's what we all want to do.") But you just have to understand that you are only allowed to have sex if it's meaningful. Erica Jong zip it up.

But what is meaningless sex? Shut up, the person at the back who said "wonderful". But it does tempt one to misquote Woody Allen, "Is sex meaningless? Only if it's done right."

Of course one of the reasons that has been put forward as to why the British are so coy about defining - or achieving - meaningless sex is just the fact that they are no good at it. Talking about the new American film One Night Stand (you get the idea what it's about), the Evening Standard concluded yesterday that the British answer to it was Brief Encounter - the film about extra-marital sex in which, er, no extra-marital sex takes place. Mind you, there are a lot of trains instead - which probably sounds far more exciting to the average man than the hassles of an affair.

Asking people what meaningless sex is like is a bit like enquiring about headlice. Everyone knows a friend who's had it but, no, they've never had it themselves. But that doesn't mean they don't think they know what it is. Intensive research suggests the following: that it's when you a) weren't in love with the person you slept with (woman's definition); b) couldn't remember her name the next day (man's definition); c) not perfect but better than nothing (desperate man's definition).

But is that good enough in the post-Freudian age? Keith Beach, a clinical psychologist and psychotherapist, brings other insights to bear: "Every aspect of behaviour has a meaning. Freud taught us that things which appear to have no meaning and were not connected were always connected in the human mind... So we may just imagine that it's physical gratification or psychological gratification but I really think we have to ask what we mean by meaningful. Or, indeed, what we mean by sex."

Er, right. But there's meaningful and meaningful. The young Damian may think it's something that can only happen in a long-term relationship and it's an expression of intimacy and love.

But Madeleine St John knows about long-term relationships and how they can offer meaningless sex, but big time. In her Booker-shortlisted book, The Essence of the Thing, she describes how Jonathan tells his live-in partner Nicola one Thursday that it's over and he wants them to split up. Nicola is aghast. "Can you remember," she says, "when you last made love to me? ... last Monday night. Three nights before you told me to get on my bike. Which means that in only three days, just three days..." "Oh that," Jonathan replies, "that meant nothing."