Visible crew/equipment: At the end of the film when the four trainee constables find the villains hideout in the derelict house, PC Potter falls from the landing to the hallway. You can see the mattress put there for him to land on. It was not there in the previous shot.
Other mistake: Early in the film Sgt Wilkins goes into Inspector Mills' office leaving Thurston dealing with the public at the counter. When Wilkins comes out of the office, exactly the same dialogue is repeated by Thurston and a man making a complaint about dangerous driving .