I can’t see what they need teachers or sex educators standing up and pontificating for,” says Stephen Green of Christian Voice. “I don’t want my children taught by people whose moral standards are different from ours. What gives these people the right to do that?” He has four children aged between nine and 15, all of whom he has withdrawn from sex education classes at their London schools.

Christian Voice claims to represent a biblical Christian viewpoint. While some object to sex education on the grounds that it corrupts children’s innocence, Mr Green rejects what he calls a Rousseau-ish theology of childhood. “The reality is that man is born evil, and the structures of society restrain him,” he says. “And the more you tell children, the more they’re going to want to experiment.”

Although fundamentalist in his expression - he speaks of the “anti-Christ, anti-God views” of sex educators - Mr Green is far from alone in his distaste for sex education.

One strong strand in anti-sex-education thinking is the belief that it undermines traditional morality, and the family.

Cornelia Oddie is deputy director of Family and Youth Concern, a secular organisation claiming members from different faiths. She objects to the neutral and non-judgmental values which many sex education resources strive to attain. “Marriage must be part of the sex education package, and it should be given as the optimum relationship, as an ideal to aim for,” she says. “As sex education tries to equalise all sexual relations, the moral aspect has gone out of it.”

It’s a concern echoed by Fred Naylor of the Parental Alliance for Choice in Education. He sees sex education as the means whereby society will eventually be morally re-structured, but not, in his view, for the better. “Undermining the old morality paves the way for the new one,” he says. “The politics of sex education is really to break up the transmission of family values through the family.”

Many have reservations about current forms of sex education on the grounds that it may put pressure on teenagers to have sex, or at least pretend to. Alison Farnell of Christian Action Research and Education calls for more attention to be paid to giving teenagers the skills to resist sexual pressure. “I think it’s tremendously important to teach kids to stand up for themselves and what they think is right,” she says. “There’s a lot of assertiveness about for sexual liberty. But not for abstinence.”

Most of the anti lobby profess themselves happy with the human biology aspects of sex education. It is not body parts but human relationships that excite controversy. Stephen Green has a further, novel view on the undesirability of sex education. “In secondary school, it’s a vehicle to promote promiscuity by contraceptive manufacturers,” he says.