I used to have a copy of a game, bought used circa 1998, single hardcover manual, called "Advanced Roleplaying" (if I remember correctly). The cover was a reddish illustration of a wizard summoning a bull-headed demon in a pentagram. I thought some interesting parts of it were historical realism in terms of medieval occupational / caste systems, thorough Catholic-based magic system and European folkloric monsters. As far as I can remember, the names of the creatures, demons, angels, etc. were all drawn from historic references (Monopods, Baphomet, Michael, etc) as opposed to being references to either recent fiction or of the author's creation. There was a traits table where a PC might randomly be determined to be homosexual, Jewish, left-handed, ambi-dextrous, etc., with nearly a hundred entries. In addition to D&D-like characteristics, characters had vices that might lead them into sin. There was some kind of sin and damnation system with sins of various severity. Magic involved either praying for miracles, or summoning demons or angels, maybe Fae Folk. Summoning anything, under any circumstances, almost always counted as a sin of some kind.
The game was reminiscent of the Darklands computer game, except more UK / Arthurian in focus. For obvious reasons, Googling "Advanced Roleplaying" doesn't produce anything useful. If anyone can provide an author, publisher, etc. that would be very helpful.