I've always been a bit unsure of the Seventies M.R. James adaptations by Lawrence Gordon Clark. On the one hand, it was good to have MRJ stories on the telly, of course. But on the other, I felt they were a bit unscary and ponderous. That said, having just rewatched the BFI DVD, I was pleasantly surprised to find that the first - and most-praised - LGC film is rather good.
'A Warning to the Curious' is a condensed but faithful adaptation of MRJ's best late story. It's an odd sort of tale, not least because the ghost of William Ager seems to vary in strength and other powers from scene to scene. But the film is carried to some extent by some very good performances, especially Peter Vaughan in the lead role of Paxton. It's clever of Clark to change the character from a, young lonely but fairly wealthy antiquarian to an unemployed amateur with worn shoes and a shovel strapped to his suitcase.
Also excellent is Clive Swift as Dr Black, who befriends and helps,but cannot save Paxton. I still have problems with Ager, though, who is presented as a mad yokel before and after his demise. Anyway, here's the first ten minutes or so.