The British Board of Film Classification
Restricted 18
To be shown only in specially licensed cinemas, or supplied only in licensed sex shops, and to persons of not less than 18 years.
The 'R18' category is a special and legally restricted classification primarily for explicit works of consenting sex between adults. Films may only be shown to adults in specially licensed cinemas, and videos may be supplied to adults only in licensed sex shops. 'R18' videos may not be supplied by mail order.
The following content is not acceptable
Any material which is in breach of the criminal law, including material judged to be obscene under the current interpretation of the Obscene Publications Act 1959.
Material (including dialogue) likely to encourage an interest in sexually abusive activity (eg paedophilia, incest, rape) which may include adults role-playing as non-adults.
The portrayal of any sexual activity which involves lack of consent (whether real or simulated). Any form of physical restraint which prevents participants from indicating a withdrawal of consent.
The infliction of pain or physical harm, real or (in a sexual context) simulated. Some allowance may be made for mild consensual activity. Penetration by any object likely to cause actual harm or associated with violence.
Any sexual threats, humiliation or abuse which does not form part of a clearly consenting role-playing game. Strong abuse, even if consensual, is unlikely to be acceptable.
These guidelines make no distinction between heterosexual and homosexual activity.