Condoms, pregnancy tests and morning-after pills are being offered in schools to hundreds of thousands of children, some as young as 11.

Twenty-nine per cent of secondary schools in England now have sexual health clinics with one in 20 providing children with prescriptions for a variety of contraceptives - the pill, injections or implants - without their parents being informed, according to research by the Sex Education Forum.

Lucy Emmerson, a senior development officer at the forum and author of the study, professed herself delighted yesterday 'that so many schools have got as far as this - not just thinking about setting up a service but delivering it'.

Her work, the first national survey of its kind, will be published on Tuesday by the forum, an umbrella organisation which supports the development of sex and relationship education in schools.

The figures have been made public just days after the government disclosed that in England and Wales there has been a 10 per cent rise in the number of abortions among girls under 16 and a 21 per cent rise for those under 14, prompting calls for mandatory sex education in schools, with five-year-olds learning about relationships.

Thirty MPs have now signed a motion calling on schools to do more. Some still restrict sex and relationship education to the legal minimum, teaching children no more than the mechanics of human reproduction in science lessons.

Critics have argued that too much information about sex and medical support in school simply encourages children to become sexually active. But Emmerson insisted that was not the case in the schools running clinics. Contact with health professionals could lead children to choose not to have sex, she said, or to at least use protection.

Her study found that all the schools offering services provided at least condoms or pregnancy tests. One in six of all secondary schools gave pupils access to the morning-after pill or tests for sexually transmitted infections such as chlamydia.

Emmerson admitted that head teachers were nervous about how parents would react. 'Some of the barriers are more a perception than a reality,' she said. 'But schools can take confidence from this report that they are not alone if they set up on-site services. In fact, they are joining hundreds of others.'

Many heads had found a discreet area in the school to base the clinics so that pupils felt confident about entering them. While the majority provided services for under-16s, health professionals took extra care with younger children, providing education and advice as well as practical services, the study found. Children were encouraged to tell parents about their treatment.

Biddick School Sports College, in Sunderland, recently announced that it would run a pilot project offering chlamydia screening to older pupils. Richard Wilkinson, the head, said he was responding to a presentation by local authority officials who warned that the disease, which often had no symptoms, could leave pupils infertile if untreated.

Others have been providing services for much longer. Callington Community College in Cornwall has had a clinic on school grounds for 13 years. Pupils can obtain condoms, the pill, the morning-after pill and chlamydia tests as well as other medical treatment, though those wanting a contraceptive injection or implant would be referred to a local health centre.

Dr Jon Tilbury, the GP who runs the clinic, said it gave children the chance to seek support confidentially. 'In Cornwall, if pupils go to the doctor it is likely to be someone they have known for a long time, who knows their parents, and there is a chance they will see friends and relatives in the waiting room,' he said.

The decision to prescribe the pill, he said, would not be based on age but on the patient's understanding of the treatment. 'It is a question of their competence to give consent. You may have someone who is 14 and does not understand the nature of the pill so we would not give it to them. But you may have someone who is 12 or 13 who does.'

Andy Hibberd, co-founder of the Parent Organisation, a support group, said: 'It is not a problem that children are getting sex advice in school but the fact that parents are being intentionally cut out of the loop is wrong. If they want the morning-after pill, the school will sanction that and the parent will never know. We would say that this is the end of innocence.'