After spending an estimated £30,000 of his children’s inheritance unsuccessfully fighting a £100 speeding fine, retired engineer Richard Keedwell has lost a lot. But little did he expect that his quest to challenge the “unfair” fine may have helped uncover an error in the system that could save thousands of unlucky motorists hundreds of pounds.

Mr Keedwell, 71, from Yate in Bristol was accused of driving 35.4mph in a 30mph zone while out Christmas shopping with his wife in Worcester in November 2016.

However he was so convinced that he was not speeding at the time that he spent two and a half years attending seven court appearances to fight the fine issued by West Mercia Police.

Mr Keedwell, a father of three sons, hired an expert witness in electronics and radar, Tim Farrow, who analysed the images of him allegedly speeding and said that he could have been caught out by a malfunction with a speeding camera known as the “double doppler” effect.

This occurs when the camera’s radar measuring the speed of a passing car accidentally deflects onto a second vehicle travelling in the same direction.

As the distance between the two cars changes the “doppler shift” is created, which makes the camera record the second vehicle as travelling faster than it is. Physicists commonly explain the doppler effect by how it causes the sudden change in pitch in a passing ambulance siren.