Dr Jack Lambert, a consultant in infectious diseases, told the Sunday Tribune that a "substantial number of 15-year-olds" and other underage teens present at sexual health clinics for treatment. Most lie about their age to secure treatment and give false phone numbers and addresses preventing medics from offering proper follow-up care.

At present, the law allows people 16 years and older to consent to medical, surgical or dental procedures. Children below that age are supposed to be treated only with the consent of their parents or guardians.

"We treat patients at the STD clinics that we're really not allowed to see, " Lambert said. "It's all kind of done on the sly. Some times they just want to come in for a check-up if they've been sexually active; other times they are coming in with symptoms."

Lambert cited chlamydia . . . which can cause infertility in both men and women . . .as "the biggest problem in this age group".

Unlike in Britain, there are no clear guidelines here regarding the treatment of minors for sexually transmitted infections.

Sexual health experts told the Sunday Tribune that clinics are unwilling to admit to treating minors as attracting attention to the practice could make services more strict, to the detriment of patients.

A spokeswoman for the Irish Family Planning Association said health professionals in statutory and voluntary agencies who are providing medical service to people under 17 are operating without adequate legislative support.

"In effect, doctors and other health professionals are operating in a legal 'grey area' in providing health services to minors at present, " the spokeswoman said. "We recommend that this needs urgent attention."

The organisation said that while provision needs to be made for cases of sexual abuse, "provision also needs to be made for those who are involved in consensual sexual activity below the age of 17 and for those who provide services to them."

Fourteen percent of Irish teenagers have or will contract an STI by the age of 24, according to a study by condom manufacturer Durex. A third of 16- to 20-year-olds have had unprotected sex without knowing their partner's sexual history.