Prior to the establishment of UK state censorship implemented in the Video Recordings Act of 1984, censorship was in the realms of the courts and the Obscene Publications Act. This required the courts to apply the test of whether videos were likely to "deprave and corrupt" the viewer. The Director Of Public Prosecutions (DPP) maintained a list of those videos that were felt likely to be found obscene by the courts and hence worthwhile prosecuting.
Of course, the real drivers behind the moral panic were the UK press led by the ever obnoxious Daily Mail. Not to mention a few politicians who felt they could make a name for themselves.
Several versions of the video nasty list were published with videos added and removed over the period 1983-1985. 72 videos were listed at least for a while. Another couple of films can stake a claim via a shared name with listed films. 39 made it through to the end, and these became known as the DPP39s. These 39 titles became the most sought after collectibles.