SEXUALLY explicit comics, TV and videos are the major source of sex education for the nation’s youth says a new report on teenage sexual behaviour.

The report damns the government’s reluctance to act over sex education, which is not on the curriculum, despite a rising number of sexually active minors (under-18s) and soaring rates of sexually transmitted diseases among them.

In the biggest survey of sexual behaviour among minors since the 1970s, the Japanese Association for Sex Education found that one in three high school students has had sex.

This is up an average of 15 per cent from the association’s last report in 1993. Only about half of those who said they have had sex used contraception.

The latest survey covered about 5,500 teenagers from 58 middle and high schools and universities across the nation. The association argues that sex education should begin at primary school.

Sex education is left to the discretion of individual teachers. There is noteaching about the contraceptive pill, nor is the “morning after” pill available to those under 20. Few parents would even dream of bringing up the subject at home.

While the government has said little on what it regards as a sensitive topic some ministers have criticised parents for neglecting their responsibilities to guide children in these matters.

Although teenage mothers are rare in Japan, some experts say the startlingly high abortion rate - half of all pregnancies are thought to be terminated - can be attributed partly to the paucity of sex education.

Schools are, however, making an effort to stem the growing tide of teenage prostitutes who meet clients in “telephone clubs” and offer them sex or companionship in what is known as “compensated dating” or enjo kosai.

Common in Japanese cities, the clubs provide rooms where men pay to chat on the telephone to females, who are often young. In Tokyo over a third of high school girls say they have used them.