The director was living next door to the pub (The New Inn) used in the movie. The pub's run-down state upstairs part inspired the feel of the story. The New Inn in Hadlow Down, East Sussex still has all the creepy, weird and haunting artwork upstairs from the film shoot.
During filming, paranormal activity was captured and used in the final cut. This can be found when Jason (Robert Vernon) is in the manor house. What you see on screen actually happened. And not just once. It actually happened on cue three more times.