More Than Mortal by Mick Farren
Something very strange and potentially powerful and dangerous has been unearthed in a prehistoric burial mound in southern England. Renquist is lured to the U.K. by a trio of devious female Nosferatu to see the mystery for himself. He discovers that the being emerging from a centuries-long hibernation in the mound is Merlin - and he definitely differs from his reputation as the benign wizard of Camelot. He is something as non-human as the Nosferatu. To complicate matters, a wild and barbaric clan of Scots vampires kidnap the sleeping Merlin and wake him - and then all hell breaks loose.