Motorists using the electronic tag system to cross the Tamar Bridge are being urged to check their accounts after it was revealed that a small number of cars are wrongly being charged for towing trailers.

Bridge staff say the errors arise from the way in which the scanning system is set up to prevent fraud and that fewer than 10 incidents are reported each month out of the 400,000 crossings – mistakes can easily be rectified by checking the photographic images relating to each transaction.

The problem was revealed after Cornish Times readers expressed concerns that when they checked their accounts they had been charged for crossing with a trailer, doubling the 50p charge to £1.

One local man said this week: 'I don't even have a tow bar on my car!.' He confirmed that when he contacted the bridge office he had no problem obtaining a refund.

Tamar Crossing manager David List said the scanning equipment installed on the toll booths was set up to recognise the number of axles on each vehicle and was intended to prevent fraud.