A sex education pack for schools that features bondage and wife-swapping has been criticised by a Christian pressure group.
Taking Sex Seriously, produced by a Liverpool firm and aimed at secondary school pupils, includes a lesson on "the full range of sexual activities".
It is currently out of print but is still recommended by local education authorities.
On Thursday the Christian Institute (CI) said it is "quite simply the worst thing ever published for sex education for schools".
The pack, produced by education firm Healthwise, was published from 1995 to 1999, and is included in a CI report on sex education to be published on Friday.
We want young people to think these things through in the safe environment of a classroom
Activities suggested for discussion include "sadism and/or masochism", "multiple partners at one time", and "partner swapping".
Colin Hart, director of CI said: "There are something
like 6,000 copies in existence.
"It is shockingly explicit and we think it should never be used in schools.
"What we want is for more consultation with parents to decide what their children should be learning about and to protect [them] from this sort of inappropriate material."
However, James Kay, chairman of Healthwise, said it was better for children to learn about sexual practices in the classroom than in uncontrolled ways.
He said: "Our approach is to promote empowerment of children.
"We want young people to make powerful decisions by having the opportunity to talk and think these things through calmly with adults in the safe environment of a classroom, not huddled in the playground or while drunk at a party.
"Sex is right in the face of young people. We're not introducing it to them but picking up something that is already there and putting it into a sensible, adult context."