As Randy said it was illegal to sell hardcore in the UK until the BBFC lost a legal challenge in 2000. After that some hardcore titles classified R18 could be sold through licensed sex shops. My take for what it's worth :-

In the 1970s and 80s some hardcore was shot in the UK but as you can see from the list of 70s Brit porn at BGAFD much of it was made for or by distributors in continental Europe and the US. There was a black market which circulated imported and home shot films in the UK (in much the same way that soft drugs were distributed) but unsurprisingly these networks have left little trace. Most UK domestic production was of softcore. The hardest locally produced film material on open sale in the early 70s were probably the near 'hard soft' one reelers made by Russell Gay's Mistral and Astral films.

Before the industry consolidation associated with the development of the 'top shelf' in newsagents on the one hand, and vertically integrated mail order companies and sex shop chains on the other, softcore production had involved some regional and 'cottage industry' production. It's likely some hardcore was also produced on this basis but it's left just as little less trace as the black market networks which distributed it. Industry history, based on looking at advertising, catalogues and whatever 'facts' were revealed during prosecutions doesn't have a lot to go on in this sort of area.

It should also be pointed out that a good part of the UK demand for 'harder' material was met by selling fake hardcore - softcore packaged as hardcore magazines or films on the basis that few punters would have the bottle to complain.

John Lindsay made hardcore for export in the early 70s. After he was prosecuted and acquitted in 1974 and again in 1977 he first opened a shop and small mail order operation and sold his hardcore films openly, and then set up a chain of private members clubs to show hardcore (exploiting the same loophole that had previously led to the creation of a lot of 'clubs' in former cinemas which showed 'hard' softcore and cut hardcore). In 1983 he was jailed after another trial and sold up. The 'cinema club' loophole was closed shortly afterwards. I don't know whether he produced many actual films in the 1980s or just repackaged his 70s material.

Mike Freeman who had made softcore in the 60s, but been jailed for murder for most of the 70s, started Videx on his release to exploit the fact that video wasn't covered by the Obscene Publications Act. He made and distributed 20 odd hardcore videos through mail order rental before he was also prosecuted in 1983 alongside a young Lindsey Honey (later aka "Ben Dover"). Although acquitted he moved to Holland.

These prosecutions were part of a general crack down in the early 80s which, amongst others, saw members of the Holloway family (Reuben Sturman's UK partners), the Gold family and David Sullivan prosecuted and imprisoned, and saw many others leave the country, to join those who'd already left after the fallout from the London police corruption trials in the late 70s. As hoped, this all had a chilling effect on any notion of domestic hardcore production. Although in reality a black market in video hardcore continued in the UK after the crackdowns in the early 80s, it consisted of pirated copies of continental and US films.

In short there was no significant UK hardcore production in the 1980s - quite apart from the legal situation it simply couldn't compete with US star power or continental willingness to push content limits.

Lindsay Honey reportedly took over some of Videx's assets and the mailing list but operated pretty much below the radar until his emergence as "Ben Dover" in the mid 1990s. As 'Ben' he made softcore versions of hardcore for open domestic sale and hardcore versions for export (and under the counter distribution) - but more importantly he created a recognizable brand thereby helping lay the basis for today's UK industry, which produces arguably some of the most inept and incompetent porn in the world.

If you want a list of 80s productions you'll probably have to research one yourself. The film listings at BGAFD are an obvious starting point. There are also a lot of useful threads and knowledgeable people in the BGAFD forums and at the
Vintage Erotica Forum. The searchable database at lists videos released before the 1984 Video Recordings Act - here are their listings for Videx.

Mike Freeman who is quite a character
has a very NSFW blog, still sells porn (including a couple of his 80s titles I think) and is publishing his entertainingly graphic memoirs, 'I Pornographer' via amazon kindle. So far he's up to volume three - volume three covers the creation of Videx in the early 80s. and stops just before the 1983 prosecution (for making gay porn - same thing they successfully prosecuted John Lindsay for) which led to him leaving the country.