The scandal over the 52-page book led directly to the introduction of Section 28, which made it illegal for authorities to promote homosexuality.

Professor Reiss, editor of the Sex Education journal, believes it also prompted the demise of the Inner London Education Authority. “Without a doubt, the book led to a coalescing of Conservative views,” he said. “It played into the hands of the Conservative government, which was convinced local authorities were getting in the way of educational development. ILEA was the most powerful and the biggest.

Politicians seize on incidents and build them up. This book probably led to the demise of ILEA.”

The authority was disbanded in 1990 and split between the London boroughs.

Professor Reiss believes these smaller authorities were unable to deal with the high rates of staff and pupil turnover. “It took 10 years for London’s education to get back to where it was when ILEA was at its height,” he said.

The general feeling about Section 28 was that the Government had banned talking about homosexuality.

Professor Reiss said: “Most teachers decided they had better not discuss anything that wasn’t to do with straight sex. So they stuck to safe areas such as the biology of sex and shied away from issues such as masturbation, gay sex or sexual abuse.”

Section 28 was repealed in 2003. But Professor Reiss believes its impact is still felt today. “Parents tend to be very supportive of sex education in schools,” he said. “But they’re hesitant still about anything to do with homosexuality. They think it might make their children more likely to experiment.”

Most schools now choose to tackle the issue during discussions about homophobic bullying. Others introduce it during debates about single parents and family diversity. “It’s amazing to look back 20 years and think about the things we got hysterical about,” said Professor Reiss. “You just don’t get hysteria like you used to. Very slowly, our society is becoming more accepting of difference.”