When Alison is driving her cart past Colpeper's house the frame cuts to a scene where he is working a field behind the house to give the impression that it backs on to farmland, which is not the case in real life.
A camera operator's shadow is clearly visible while Alison is riding a horse and buggy along the pilgrim's road.
When Sergeant Johnson is adjusting the mirror in his room at the Hand Of Glory inn the wire manipulating the mirror is just about visible at the bottom rear of the mirror.
Colpeper appears at the garage in Canterbury where Alison keeps her caravan although the address of the garage was not mentioned when they met earlier. (He's familiar with Portal the owner, however, so an old caravan may have been mentioned to be there at some point and Colpeper links the two.)
Gibbs refers to the character portrayed by Charles Hawtrey as George. His given name as listed in the closing credits is Thomas.