Sex, so the old joke goes, is what well-heeled ladies used to keep their coal in. No more. In the most revealing survey ever carried out into Britain's sexual habits, we are having more sex, more often and with more partners than at any time in our history. This does not trouble us. For a nation once regarded as the most sexually repressed in Europe, we are also increasingly relaxed about using prostitutes and open about experimenting with homosexuality.

This is not simply the talk of boys and girls in bars bragging about their conquests. The National Survey of Sexual Attitudes and Lifestyles 1999-2001, released last week, questioned 11,000 people over two years. The findings provide the most accurate cross-cultural picture of sexual behaviour to date. The average age for first sex is now 16, though 30 per cent of boys and 26 per cent of girls do not last out that long.

Respondents filled in their answers on laptop computers in their homes, making the researchers confident about the levels of honesty. While the fact that there is more sex going on is good news for the hordes of young and not-so-young people prowling bars and clubs in search of a new sexual partner, there is, sadly, a downside. Although young Britons may be more at ease with them selves about sex, they are also less knowledgeable about how to prevent pregnancies and sexually transmitted diseases than anywhere else in Europe.

The problem lies with boys, though it is not their fault. Sex education lessons at school are not stimulating enough, concentrating too much on biology and not enough on preventing disease and pregnancy. More than 90,000 teenagers get pregnant every year; last year 7,700 were under 16, and 2,200 were under 14.

Simon Blake of the Sex Education Forum believes the heavy emphasis on reproduction during sex education means 'boys are just switching off because it is difficult for them to see any of it as relevant or beneficial'. Nationally, male teachers are in short supply and men are less keen to teach sex education. Taught by women and focused on girls, the system perpetuates the idea that sex education isn't 'man's stuff'.

Nor will boys get told enough at home. They do not have the same obvious physical stages of development as girls, and mothers, who traditionally give most advice, often know less about male development too. Fear of pregnancy makes talking to daughters seem like a more urgent issue. Boys are often just left to 'sow their oats', with parents simply hoping they do it carefully.

Ollie is a typical example. The 17-year-old is in the lower sixth at a mixed private boarding school in Wiltshire. He was given leaflets when he was 13 and learnt about contraception in GCSE biology. He thinks it would be better if boys had information on sex when they were much younger. 'It would be less embarrassing than getting it at puberty when everyone is feeling so weird anyway,' he said.

He has tried to sort out his own protection. Like the 76 per cent of 15 and 16-year-olds who told a Durex survey that boys should always carry condoms, Ollie has some difficulties getting them.

Vending machines in public toilets provide some discretion, though teenagers like Ollie who live in the country often have to rely on their parents to drive them into town. He has to sneak off and buy them furtively.

These problems are spawning an epidemic of sexually transmitted diseases. Dr Kevin Fenton, senior lecturer in epidemiology at the University of London, has been tracking the outbreaks. Urine sample taken randomly showed that one in 45 men and one in 66 women were infected. Most of them were completely unaware of the fact because many sexually transmitted diseases do not have any symptoms. Carriers go untreated and the diseases spread through the population. And so the cycle goes round.

Chlamydia, a bacterial infection, is one of the biggest causes of female infertility. Young women are routinely screened for infection; men are not. It does not make sense to concentrate resources on women if so many men are carrying infections.

This is not to say schools are not trying. Some teachers encourage peer education. Adolescents suggest that they prefer this because their peers tend to be 'nicer' to them, but this may simply indicate that they are willing to learn from anyone who treats them with respect and honesty.

Alex, also 17, last month went to a school lesson on men's health. It was successful because it was given by a doctor whom none of the students knew. Alex feels sex education is embarrassing if you know the teacher.

Despite our apparent boldness in sexual adventure, we still like to have sex in private. As with sex, so with sex education. The state should support an online sex education programme that could be accessed at home or school. In private.

Suzi Godson is the co-author of the forthcoming Sex Book (Cassell, May 2002)