Factual error: Both Inspector Shaw and Chief Inspector Bailie wear their medal ribbons in the wrong order. The Golden Jubilee Medal is worn first, followed by the Diamond Jubilee Medal, followed by (for Bailie) the Long Service and Good Conduct Medal.
Factual error: The detective constable is addressed as "Sir" by uniformed constables. They actually hold the same rank. Detectives do not outrank uniformed officers in Britain.
Continuity mistake: When Nick's mom tells him to show Gypsy around she takes the cigarette away from her lips. A shot later it's back in.
Factual error: Detective Chief Superintendent Kier Pritchard wears silver tabs on his uniform collar. These are only worn by Assistant Chief Constables and above. Detectives almost never wear uniform in any case.