The Body Beneath (1970)

One rainy day in London on the edge of Hamstead Heath, there's a knock at the front door of the Ford family home. Unknown to any of the Ford household, the Reverend Alexander Algernon Ford, is actually the head of a large family of ancient vampires also named Ford, who are on the hunt for fresh blood because of constant intermarriage between the vampires over the centuries has seriously diluted their blood line. The vampire "reverend" has his eyes set on a particular relative, Susan Ford, whom he plans to kidnap. He intends to indoctrinate her into his secret coven and use her as a breeder in order to stay in existence. How will Susan be saved?