By Thrasy Petropoulos

For somewhere that routinely supplies contraception to girls as young as 12, advises on terminations and carries out tests for sexually transmitted infections (STI's), the Euston branch of the Brook Advisory Clinic is a remarkably inconspicuous place.

To the left is an abandoned shop with a month's worth of letters piled on the carpet and to the right a dust-ridden electronics outlet, complete with outsized satellite dish on the wall.

And between the two, a series of frosted-glass windows displays only an address and the words "Brook: Putting Young People First."

But throughout the week hundreds of people drop in unannounced for free and confidential sexual health advice for those aged under 25.

Today I gave out half a tonne of condoms to girls who were not practising safe sex

Dr Gillian Vanhegan

Most seek contraception, some need pregnancy tests and counselling on abortions, but all are encouraged to be tested for STI's.

The upshot is deeply concerning.

Many of those who volunteer to be tested are finding that they are carrying an infection, despite appearing perfectly healthy.

Common infection

Chlamydia, the most common STI in the UK, is virtually symptomless in 70% of infected women and 50% of men.

A typical consulting room

And with the growing numbers of positive results at Brook clinics around the country, one leading doctor has revealed her fears that we are heading for a generation of women with serious fertility problems.

The most surprised are always the men and women concerned.

Take the case of a typical 15-year-old girl who drops into the clinic in Euston, central London - let's call her Sophie for the sake of anonymity - fearing that she is pregnant.

Though she does not have an appointment, Sophie is first given a private consultation and encouraged to give details - always hand-written and never entered into a database - of her relationship with her partner and parents.

Eventually she is called from a waiting room - by her first name, as is policy - and a nurse confirms that she is indeed pregnant.

Digging deeper

The next stage is to see the on-site counsellor who delves further into her situation and determines whether she should go ahead with her desire to terminate the pregnancy.

The fear seems to have gone out of HIV

Dr Gillian Vanhegan

As Sophie is under 16 and adamant that her parents should not know of her situation, the counsellor is entitled by law to determine whether she is mature enough to make such a decision.

Given the immaturity of some of the girls who visit the clinic, not to mention the inability of many from the large transient population in the area to even complete a standard form giving personal details, the counsellor has no problem in agreeing to Sophie's request.

It is now that she is told of the importance that she be tested for STI's, particularly chlamydia.

Not only are there long-term risks for women - pelvic inflammatory disease, which can lead to ectopic pregnancies, infertility and chronic pelvic pain, and pneumonia and conjunctivitis in their babies - but chlamydia-sufferers risk massive complications if they undergo abortions before being treated.

The test, again on-site, is sent away for analysis and a week later the doctors' fears are realised when the results prove positive.

Spreading infection

Sophie was lucky, but countless men and women carry on their daily lives unwittingly carrying and spreading chlamydia.

That Sophie became pregnant clearly reveals that she was not practising safe sex, despite not wishing to become pregnant.

Dr Gillian Vanhegan, the medical consultant for Brook, does not mince her words when she talks about the issue.

"The problem is probably due to the increased number of sexual partners girls have," she said.

"Today I gave out half a ton of condoms to girls who were not practising safe sex.

"The fear seems to have gone out of HIV.

"They are looking out of the window and noting that there is no Aids epidemic. People aren't dropping dead by the thousands, as those awful advertising campaigns in the Eighties had predicted.

"They think they are no longer at risk."

No improvement

And the work done at the centres clearly shows that problem with teenage pregnancies - the UK has the highest number in Europe - is not improving.

"The government have as their aim to halve the teenage pregnancy rates by 2010, but the figure went up in 2000 and though it has come down slightly during the last year it has only done so by something like 1%," Dr Vanhegan said.

"We have been offering chlamydia screening for two to three years. It so happens that its peak is in girls aged 16-20 and young men aged 20-25, but there has been a 106% increase in diagnoses since 2001.

"Partly that is a result of the increased testing, but it also reveals the extent of the problem.

"The government have put nowhere near enough funding into it. We're lucky in London where we have two clinics, but a girl in a random part of South Wales, who only has her stuffy GP to go to, will often feel completely isolated.

"And once you've been screened and positively diagnosed you have to trace the partner or else there is virtually no point in treating the girl.

Willing to cooperate

"Naturally, the confidentiality of the patient is paramount but virtually all girls are accepting and willing to cooperate.

"We give them letters addressed to their partners explaining what they need to do. The frustrations begin when the girls have no idea who the partner that gave them the infection is, or where to contact him.

"And even if the man is given the forms, more often than not they go into denial, saying that they must have been infected by someone else.

"Naturally we test for and treat other STIs, such as gonorrhoea, but testing for chlamydia is of paramount importance because it shows virtually no symptoms.

"I don't want to sound alarmist but I think that in 10-15 years' time we are going to have a serious problem with female infertility in this country.

"In 70% of cultures grown from fallopian tubes from women at infertility clinics, chlamydia is found to be present."