The job of overseeing personal, social and health education, which includes teaching about sex, is often left to a relatively junior member of staff, typically a young woman.

They can feel isolated, bearing the brunt of parents’ concerns, as well as the anxiety, and even aggression, of other staff who feel uncomfortable taking the subject.

The two-year study carried out in 17 secondary schools by University of Keele researchers found that both teachers and pupils are aware of the debate about sex education and that the sensationalist views of some politicians and media increase anxiety in lessons.

The report, presented to the British Educational Research Association conference last week, said that heads may choose to delegate responsibility for PSHE in order to avoid any tricky issues.

All secondary schools are required to teach sex education from Year 9 and can choose to start it earlier, although parents can withdraw children from lessons.

Researchers found that sex education is a low priority for schools more concerned with boosting their exam performance.

The typical budget for the whole of PSHE - which includes health, careers and drugs education, as well as sex education - was pound;500.

Consequently, the role of PSHE co-ordinator is seen to have low status. When combined with the prospect of dealing with reluctant teachers, nervous governors and awkward parents, this led to few teachers being willing to occupy the post for a sustained period.

One “very successful” PSHE co-ordinator told researchers: “No, I would not do it again. It is a lot of hard work, very little appreciation from anyone else and because there are a lot of staff who do not feel comfortable about teaching it, you are the one who gets it in the neck because they are angry about it.

“Where staff or pupils are not happy about it, or are threatened by it, it can come out in aggression.”

The report said: “The job needs better rewarding to keep experienced staff specialising rather than the poisoned chalice being handed on to someone new every year or two.”

Teachers often felt under-prepared or uncomfortable taking the lessons and resented having to do what they saw as a job for parents. Older and male staff tended to be more uncomfortable than their younger female colleagues.

Staff were also concerned about imposing their own morality on to lessons and said that more training should be available.

“You are a form teacher and you do not just want to go in and suddenly talk about sex,” said one.

Another said: “I think the biggest fear in that situation is being asked a question you just cannot answer.”

Teenage health freaks, 20

“Teachers’ views of teaching sex education” is available from m.david@keele.ac.uk