Grace lost her virginity at the tender age of 14, and regretted it at 16. “I’d been going out with my boyfriend for six months, and thought I was in love,” says the teenager. “I wasn’t really, and looking back I’m a little bit sad about it. There’s a lot of pressure from your friends to have sex just for the sake of it, and I wasn’t able to think for myself.”

That has changed now for Grace — one of 12 teenagers who took a five-month vow of celibacy as a social experiment which is currently being played out in a three-part television series on BBC2.

“It was incredible,” says Grace, from London. “I wasn’t expecting to like it at first, but we had real discussions about sex with the adults on the course rather than being lectured by teachers on pregnancy and biological basics like you get at school. We talked about the emotional side, what it should mean.”

Grace kept her pledge, went on a trip to America to meet youngsters who had taken the controversial Silver Ring abstinence vow until marriage, and says that she found the course “life-changing”. What makes her experience more than just highly watchable television is the fact that conventional sex education in the UK has singularly failed.

Britain has the highest level of teenage pregnancies and sexually transmitted disease in western Europe. The latest figures show that — despite a government promise to halve the rate by 2010 — conceptions have soared among girls under 16, the legal age of consent. Official figures show that pregnancies in England and Wales went up from 7,875 in 2002 to 8,076 in 2003 among the under-16s.

The experience of mother-of-three Jane Foot is symptomatic of the piecemeal approach to sex education in this country. Increasingly, it seems, the issue is back in parents’ hands — partly because of a confusion regarding what schools should teach.

Foot found out that a frank talk with her daughter was overdue when she found a stash of contraceptives hidden in her 14-year-old’s room. “I wouldn’t describe Maya as being by any means precocious, but she goes to a private London girls’ school where many of her friends want to look and behave like young adults,” says Foot. “I rather naively thought that the school would be guiding them to behave appropriately.”

Foot, an accountant who lives in south London, adds: “I was relieved to find out that she wasn’t having sexual relations with boys, but I was horrified to discover that she had been given the condoms by health workers at a family planning clinic, while accompanying her friend to get emergency contraception. I simply don’t agree with this approach. I feel that by handing out condoms to 14-year-olds as if they were candy, these people are actively encouraging young girls like my daughter down the path of casual promiscuity.”

At the beginning of the year, an Office for Standards in Education report condemned current sex education in Britain’s schools as “poor” while the Family Planning Association has called for it to be made a legal requirement from primary school age.

At the same time, youngsters are bombarded with sexual imagery. Last month, it was revealed that W H Smith was selling a Playboy stationery range targeted at children, featuring the infamous bunny girl logo of the adult magazine.

So how should parents protect their children? According to a spokeswoman from the sexual health organisation Marie Stopes, parents must try to establish a dialogue with their children early on. “A lot of parents assume that sex education is going to happen at school,” she says. “But there is no specific curriculum in this country.There are schools that don’t promote sex education for many reasons, including that the teachers don’t know how to teach it.

“Parents need to address this — realise that for a child, forewarned is forearmed. Just because children know about sex doesn’t mean that they are going to have sex immediately — in fact, research shows that the opposite is the case. Give your child facts — from the age of 11 — rather than fob them off.”

For Grace, talking was key: “In our sessions we talked about why teenagers are having sex, and what are the consequences. People listened to me, and I feel I really matured and grew in confidence. I learnt to think for myself.”

No Sex Please, We’re Teenagers is on Tuesdays on BBC2