A police force has let off 59 of its own drivers caught speeding.
The marked vehicles, which were being used for operational purposes, were caught by mobile cameras in Derbyshire.
Police bosses scrapped the tickets even though in at least 14 of the cases no blue flashing lights were detected by the cameras.
Some safety groups have been upset at the decision to tear up the tickets, with the charity Brake saying the decision "smacked of double standards".
Mick Creedon, Derbyshire Police's assistant chief constable, said: "Would you want us to go to the scene at 30 miles an hour and comply with the speed limit?
"Or if there's an emergency, if there's a fatal accident, if there's someone being attacked and stabbed, if we're carrying out surveillance against difficult organised criminals, do we do that at 30 miles an hour?"
The issue arose after the officers were sent notices of intended prosecution in 2004 after they were photographed speeding.
The officers' own divisional commanders and the force's head of criminal justice department examined the incidents the cars were attending and decided none of them should be prosecuted.
Supt Royston Smith said that in at least 14 of the 59 incidents, flashing lights used by the vehicles in question had not been picked up by the camera, and it has since been satisfied they were displaying their blue lights.
Kevin Clinton of the Royal Society for the Prevention of Accidents, said: "There are times when the police have to exceed the speed limit but this has to be done safely and blue lights must almost always be used to warn the public.
Brake spokesperson Caroline Chisholm said: "Officers who break speed limits make a mockery of the crucial laws of the road that other police officers work hard to enforce.
"All drivers - police officers and members of the public - have a responsibility to stay well within limits at all times because breaking the speed limit by just a few miles per hour can be fatal."
The force has recently carried out a review of driving standards and has introduced new assessment procedures.