Sounds kinda of Hammer Film-ish, but doesn't seem to exactly match any of their films that seemed a possible match. Still might be worth checking out "Twins of Evil", "The Vampire Lovers" or "Countess Dracula".
This site seems to be a good guide to the Hammer films, though the plot synopsis are minimal.
http://mondo-esoterica.net/links_pages/Hammer%20Films.htmlIt also sounds like perhaps one of the "Subspecies" films (there are 4) might be a possible match, AFAICT none of them match your description exactly.