Parents cannot be relied on to teach their children about sex, the Liberal Democrat health spokesman has said.
Prof Webb wants compulsory education
Steve Webb said all children should receive sex education at school - and parents should not be allowed to stop them attending the lessons.
Teaching about relationships should start earlier in life, in an effort to reduce the UK's high teenage pregnancy rate, he added.
And this had to be more than watching a "grainy film" in a biology lesson.
Professor Webb said more research was needed on teenagers' "changing attitudes" to sex.
He told a fringe meeting at the Liberal Democrat conference in Blackpool: "I'm opposed to children being taken out of sex education.
"We all know parents with whom sex education just isn't going to happen."
Prof Webb said the UK's pregnancy rate for girls under the age of 16 was 30 in 1,000, while it was just six in 1,000 in the Netherlands.
He argued that modern attitudes to alcohol, with teenagers drinking more, could be having an effect.
Prof Webb said sex education provision was still "patchy".
At some schools it had not improved since his own boyhood, when a biology teacher "showed a grainy video of teenagers with no clothes on jumping into a swimming pool".
Beverly Malone, general secretary of the Royal College of Nursing, said more school nurses were needed to provide sexual advice to pupils.
There were currently only 2,140 - one for every 14 schools.
Dr Malone said: "It's just not enough. There's no way to have a public health system unless we are working on the lifestyle choices of young people."