A LASER jammer device fitted to a motorist's car effectively blinded police speed guns, a court was told.

Teesside Crown Court heard the device could also deceive police officers into thinking a speed gun had failed to operate properly.

Steven Callaghan, an expert witness called by the prosecution in the trial of pensioner Eric Craggs, was invited to view two DVDs which showed a police officer attempting – and failing – to measure the speed of the defendant's Aston Martin car.

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He also carried out a check on the equipment fitted to Mr Craggs' vehicle and established it was capable of interfering with laser speed camera meters, better known as speed guns.

Mr Callaghan, who advises the Home Office on the construction and testing of police speed enforcement equipment, said the laser jammer mimicked the specific light patterns sent out and received by speed guns in order to measure a driver's speed.

“This device is deliberately programmed with the characteristics of most known laser speed camera meters,” he said.

Prosecutor Andrew Walker added: “It effectively blinds the police speed gun.”

Mr Callaghan said that ordinarily laser speed meters were accurate within one mph and could be used over a range of three quarters of a mile by an officer.

However Mr Craggs' trial has heard that twice his Aston Martin evaded detection in Stockton when a Cleveland police officer, PC Lorraine Williams, attempted to check his speed with her equipment displaying an 'error' message.

Mr Craggs, 68, of Junction Road, Norton, Stockton, denies doing an act intending to pervert the course of public justice between July 15 2009 and August 12 2013. The trial continues.