'Video Nasty' is a British term for (supposedly) shocking and depraved horror films available on video cassette.
Prior to the Video Recordings Act of 1984, videos in Britain did not have to be submitted for classification or censorship by the BBFC (unlike films intended for cinema release). As a result, a number of horror films- many of which would have been cut to shreds, or banned altogether at the cinema- were now available uncut on video.
Such films included
and many more. Often the reputation of these films (aided by gory cover art) exceeded their content. Unfortunately, this was about to backfire...
Coupled with the increased accessibility of videos to underage children, the situation was ripe for some Daily Mail-sponsored moral hysteria from Conservative MPs and guardians of the nation's morality.
The government's first line of attack was to use the Obscene Publications Act against the distribution of such material.
However, in 1984, the Video Recordings Act was introduced, stating that from 1 September 1985, all video recordings (with a few exceptions) required a BBFC certificate.
Videos were rated separately from cinema releases, as factors such as children getting their hands on such material were to be taken into account. This meant that video censorship was, if anything, harsher than that intended for the cinema.
Of the remaining video nasties that were not banned altogether, many were cut to shreds by the censors upon their reissue. The situation has eased somewhat in recent years, with the ban on many films being lifted (albeit with cuts), and many previously mutilated films being reissued with fewer (or no) cuts.
However, although the expression 'video nasty' still pops up on occasion, the context which originally gave rise to it is long gone.
References and further reading:-