Jan Barlow is perhaps not the person you expect to be head of a campaigning charity at the epicentre of a raging debate about teenagers and sex. The rows over abortion, pregnancy and sex education are invariably fiery and emotional, but if Barlow has strong personal feelings on the issue, you wouldn't know. She is almost disconcertingly rational, intriguingly self-possessed.

Barlow inherits a pioneering radical tradition at Brook, which celebrated its 40th anniversary recently. When the charity was founded by the physician Helen Brook in 1964, as a small centre in London providing contraception for unmarried mothers, it was a beacon of sixties progressiveness, sticking two fingers up to the repressive moral attitudes of post-war Britain.

Since then, Brook - like many charities born in the 1960s - has moved into the mainstream. It has a network of 17 advice centres across the country, as well as outreach programmes, helplines and a publishing arm producing educational booklets. It offers young people confidential counselling and advice on issues ranging from contraception to sexually transmitted diseases, in a "non-medicalised" environment. It is the only national voluntary organisation of its kind.

Barlow's manner may be managerial and detached, but she is adamant that Brook has not lost its campaigning edge. It has limited resources as a provider, so she believes a large part of Brook's role must be to lobby for policy changes that will help the young people the charity cannot reach. She wants government to understand why young people need advice on sex and contraception, and what sort of advice works best.

She praises the government's strategies on teenage pregnancy and on sexually transmitted infections as "steps in the right direction". But, she says, Brook would like to see "decisive government action to make sex education compulsory and comprehensive". The "patchy" sex education provision currently on offer, where it is up to individual schools to decide what, if any, sex education they provide, is "unacceptable".

With rates of sexually transmitted infections going through the roof (up by 116% in a decade), UK teenage pregnancies still the highest in Europe, and a lack of comprehensive provision for free advice on the NHS, Barlow says the services Brook offers are indispensable to more than 100,000 young people a year.

During what is an articulate - and disarmingly speedy - analysis of Britain's sexual health crisis, Barlow returns constantly to two key themes: the media's role in perpetuating the problem, and why sex education can help solve it.

"We have a completely confused and inconsistent approach to sex in this country," she says. "The front page of a newspaper might have a couple of celebrities talking in quite graphic terms about their relationship and sex, yet a few pages further into the paper a 15-year old who is pregnant will be completely demonised. This sends out confusing signals."

Barlow believes the "mixed" and "misleading" media messages add to young people's confusion about sex, and that this fosters a climate in which adults and young children find it difficult to talk honestly and openly about sex. Media coverage of sex borders on "hysterical", Barlow suggests, illustrated recently by sensationalised tabloid reports about a schoolgirl, Melissa Smith, who had an abortion at 14 and became pregnant for the second time six months later. The press also missed the bigger picture when it reported, a fortnight ago, last year's rise in the number of teenage pregnancies. She points out that the overall trend for the past decade has been downward.

Media outcries over late abortions don't help young people either, she says. Although she is not as spikily contentious on this issue as the head of the British Pregnancy Advisory Service, Anne Furedi, who last week caused uproar when she called for access to late abortions to be made easier, Barlow is sympathetic. "The number of abortions carried out after 20 weeks is a tiny proportion of the total," she says, "but it is true that young people, particularly under-16s, are more likely to seek a late abortion. That's because they are more likely to delay telling anyone about their pregnancy, or may even be unaware that they are pregnant, so their options can already be reduced. The main issue for young people is that they need to be guaranteed a quick referral for an abortion, rather than having to wait, sometimes for several weeks, taking them closer to the legal time limits."

Barlow wishes that the issues were debated sensibly by the media. "If you only followed certain sections of the media, you would think most people in the country were hysterical about sex," she says. "But what we have to remind ourselves of is that all the research and all the opinion polls show that the majority of parents do want their children to know about sex and relationships."

The way to counteract the mixed messages in society and to prevent young people being perpetually confused about sex, she says, is through "access to free and confidential sexual health services" - such as those offered by Brook, where they can get information in a private and non-judgmental environment - and, crucially, through better sex education.

She is fully aware of the worries some parents have about sex education ("stirred up by the media"), but counters by saying that so long as the information provided is "appropriate" to the age group, it is the best way forward. "I think people misunderstand what it would entail," she argues. "They may think it will be too graphic. But if it is done well, it can only help. We know that sex education gives young people the confidence and knowledge they need."

The government has spent millions attempting to reduce teenage pregnancies, and has little to show for it. So does sex education work? Barlow is convinced that it does. "Our research is backed up by evidence from other countries," she says. "Where sex and relationship education and confidential advice services go hand-in-hand, rates of both (teenage pregnancies and STIs) are lower."

It sometimes appears to frustrate Barlow that the government and the media don't always see it from this point of view. In particular, she is bemused by the recent enthusiasm in government and in the press for US-style promotion of abstinence.

Last week, the Health Protection Agency emerged as the latest advocate when it reported that teenagers were "disproportionately" affected by rises in STIs and that abstinence could be one way forward. And the government is planning to put millions of pounds into a sex education campaign for next year that will incorporate this view.

Barlow is unimpressed. "It just doesn't work," she insists. "Advocates of abstinence point to America, but it hasn't worked there, so why should it work here? Research from the US shows that there is no difference in the level of STIs among those [older teenagers] who have signed a pledge of some sort and those who haven't."

So what of the future? Barlow says: "It is absolutely essential that young people are given the best information and that they know there is somewhere they can go for confidential advice. Brook will continue to do this."

And does she hold out any hope of sex education being made compulsory any time soon? "Mmmmm. Perhaps not in the immediate future."

The CV

Age 39

Status Lives with her partner

Lives Cambridgeshire

Education Degree in modern and medieval languages from Cambridge University; MSc in development studies.

Career 1990: GP postgraduate education manager at East Anglia Regional Health Authority; 1992-1997: joint planning manager at Croydon Health Authority, and later head of corporate affairs; 1997-2001: head of corporate affairs at Save the Children.

Interests Horses in general, and dressage in particular.