When the flying squad cars enter the airfield, there are three of them, including a Ford Cortina, all ready for action. During the scene when the criminal's Jaguar & a Flying Squad Triumph clash the Cortina vanishes, but re-appears when the chase then moves to dirt tracks.
In the final chase scenes, when the police cars are chasing the robbers' Jaguar over the grassy airfield, copious amounts of mud and spray can be seen in shot, coming from the back of the camera car which is filming them.