Here's a piece on a great and often uderrated British horror film starring Peter Wyngarde. If you haven't seen it, you're missing an atmospheric little chiller with a touch of Rosemary's Baby (minus the baby!) and some superb B&W cinematography. You may know it as Burn Witch, Burn: http://fridaynightboys300.blogspot.co.uk/2014/10/night-of-eagle-sidney-hayers-1962.html
Seems like it was much more common in the 50's and 60's for British films to have completely different titles on both sides of the Atlantic, than any other decade.
The book is a great, eerie read. Fritz Leiber wrote "Conjure Wife" in the early '40s, and I think it's still in print.
There are also shades of the Hammer film, The Witches - though I prefer this; I think it's up there (but not quite on a par) with Night of the Demon, The Innocents and The Haunting.