When the police go to arrest Gavin he is in a short-sleeved dark patterned shirt, but when he comes out of the front door a few seconds later he is in a cream long-sleeved top.
Set at Christmas, all the trees and bushes are in full leaf.
When Gavin is first apprehended in his bedroom he is wearing a dark shirt. When he emerges from the front door of the house a few seconds later, he is wearing a white shirt.
When the police initially arrive at the first crime scene, the camera pans right to reveal the number-plate of the parked 'jam sandwich' police car at the bottom right of the screen. The car's plate starts with a B prefix. This plate reg was first issued on 1st August 1984, some 9 months after the events.
During the scene at the village hall, BBC Master computers are clearly visible. However the BBC Master computer was not launched until 1986.