Submission Constable Morrison said: "We saw a car behind us going at excessive speed, so I switched on the VASCAR device.
Police constable Ewan Kidd, 46, who was driving the police car, said that they then checked the VASCAR wasworkingbydrivingameasured mile at 60mph in Stirling.
PC Kidd said they completed the mile stretch in exactly a minute, which he said "proved the VASCAR was working correctly".
He told the court: "The Crown has failed to lead any evidence that the VASCAR had been checked before the incident, they failed to prove the police officer who used the VASCAR was qualified and they failed to prove the measured mile they used was indeed a mile.
VASCAR - Visual Average Speed Computer And Recorder - is a timing computer fitted to police cars and operated using a handheld trigger.
Chief Inspector Andy Orr, deputy head of road policing, said: "There is a suggestion that the VASCAR system might be affected by Airwave radio waves and the matter is currently being investigated
Road traffic lawyer Graham Walker said last night: "Anyone who has been convicted using VASCAR should contact a specialist solicitor and investigate the possibility of an appeal in connection with their case.
com, said his firm would be reviewing all VASCAR cases dating back to 2005, when the pounds 2.
The solicitor said VASCAR used to be the "main method of mass prosecution" by the police.
A spokesman said: "Road policing units with all forces in Scotland have been advised of a potential issue with three speed detection systems - VASCAR, Police Pilot and Provida.