This entry won't be about British comics. I want to recommend three European comics. They've been published in English at one point and they're very popular across the Europe, but I still feel that UK audience isn't really aware of their existence.
All I can say is: shame on you.
Let's begin with the probably the most popular title among the three. Thorgal - created by Jean Van Hamme (story) and Grzegorz Rosiński (art) has sold in millions of copies across the Europe and world. 34th album is expected to be published this year, and the series has spawned a few spin-offs, including books, audiobooks and games.
The series is widely available in UK thanks to Cinebook. However, the order of albums is slightly different when compared to the original run. Child of the Stars, which is the first UK volume, contains original issues #7 (Child of Stars) and #14 (Aaricia), which is almost alright, since both sets of stories are sort of prequels to the main story. Things get a bit more complicated with the second UK volume The Three Elders of Aran which is a combo of issue #3 (The Three Elders of Aran) and #4 (The Black Galley). Where are issues #1 and #2? Haven't been published by the Cinebook yet - although both albums were published in the past in English by other publishers. Nonetheless, the series can be highly entertaining even without first two stories. I can recommend going from first UK volume (Child of the Stars) until at least UK vol. 8 (Wolf Cub). Further albums are great too, but vol. 1-8 are simply the best of the best.
I think there's a really good chance that you heard about the next title or at least about its author. Enki Bilal - The Nikopol Trilogy. I'm not sure if Bilal is well known in UK. I think he gets some recognition, for example Comic Heroes magazine has just done a long feature about him and his work. However, it's quite hard to get his books in English, The Nikopol Trilogy is unfortunately good example. They've been out of print for a long time and used copies are getting ridiculously expensive. If you can read in French, I recommend just getting a French, thus original, album.
The third title is Rork by Andreas. The story, set in early XXth century, follows paths of Rork - a young looking 300 years old magician of an unknown origin and uknown destination. I guess you can call it a bit lovecraftian, and sometimes it's really not easy for the reader to read a story that isn't really resolved in the finale. Andreas himself is known for creating comic books that require multiple readings.
The series has gone through some changes. It started in 1978 as a series of short episodes eventually tied into a bigger plot. Then the story was on hiatus for a few years only to be revived in late eighties - and by this time Andreas has changed his drawing style a lot when compared to the first two albums.
Rork concluded in 1992, but came back in 2002 and 2012 with publication of older tie-in stories and the brand new (although again sort of tie-in) album which is also included in the integral album. It worth mentioning that something like a Rork-Universe exists and it includes another Andreas great title: Capricorne.
Unfortunately, I'm afraid that only three albums are available in English: Fragments (1990), Passages (1990) and The Graveyard of Cathedrals and Starlight (1996). Rork was also featured in Cheval Noir.