When PC Erny talks on the police radio, the voice on the other end is director Ken Russell.
The skull of the pagan god Dionin used in the movie was constructed by adding sculpted sections to a real cow skull. The original teeth were pulled and replaced with fabricated ones to simulate the serpent look. Two skulls were fabricated for various scenes in the movie.
The mouth of the White Worm (Dionin) seen in the tunnel towards the end of the movie was actually a painted over Volkswagen Beetle hood that bears an uncanny resemblance to the mouth of a snake.