The home secretary, Jack Straw, is to announce next week his plans to tighten obscenity laws after a high court ruling allowing the sale to adults of R18 videos depicting explicit consensual sex.

Yesterday, because of the ruling, the British Board of Film Classification was forced to issue guidelines permitting the legal sale of hard core sex videos.

The film censors' guidelines spell out what is not acceptable, as well as what is, in the R18 category of sex videos, which are allowed to be sold only through licensed sex shops.

Berth Milton, the chief executive of the Private Media Group, one of the largest sex video producers, said: "We think this is a tremendous opportunity for the supply of quality adult material in Britain."

The guidelines say that scenes depicting aroused genitalia, masturbation, oral-genital contact, penetration, non-harmful fetish material, and group sexual activity will be permitted.