“Teaching sex education in schools is really important, for obvious reasons,” comedian John Oliver begins. “No parent wants to talk to their kid about sex. And no kid wants to talk about sex with their parents.”

However, Oliver points out in the latest episode of his US comedy news show, Last Week Tonight, the quality of sex education varies widely from school to school.

As in the UK, US sex education is not mandated on a national basis: only 22 states require that it should be taught in their schools. Of those states, only 13 insist that the instruction should be medically accurate.

“Which is crazy,” Oliver says. “You wouldn’t accept a  history class not being historically accurate: ’Prince started the American revolution in 1984, and his purple reign lasts until the present day. Class dismissed.’”

The British comedian, whose weekly programme is screened on HBO, then runs through some of the laws restricting sex education in the US. In Mississippi, for example, teachers are allowed to discuss contraception, but are prohibited from demonstrating how it is used.

“That means no condom on a banana, no condom on a cucumber,  no condom on a zucchini,” he says. “And that’s terrible, partly because it’s fun putting condoms on produce.”

In eight states, meanwhile, laws limit what teachers are allowed to say about homosexuality. And, in Utah, the law prohibits discussion of the intricacies of sex. Instead, teenagers are expected to discuss this with their parents.

“Here’s a conversation that’s never happened,” Oliver says. “‘How are you so good at sex?’ ‘I was home-schooled.’”

He therefore recruits celebrity friends - including actor Laverne Cox, comedian Jack McBrayer and actor Kristen Schaal - to appear in his own, non-judgmental sex-education film.

“If you want to be abstinent, that’s fine,” teenagers are told in the film. “If you don’t want to be abstinent, that’s also fine. Abstinence is like being a vegetarian. People should respect your choice.”