TENS of thousands of drivers could have their speeding convictions quashed after a landmark legal challenge by two police officers this week.

North Yorkshire Police officers David Burlingham and Andrew McFarlane plunged motoring law into chaos after successfully challenging their speeding offences by proving the road signs they drove past were illegal.

The move could open the floodgates for thousands of motorists getting their convictions quashed with police forces forced to pay back millions of pounds in fines. Endorsement points and driving bans may also be wiped out.

Traffic officer Burlingham, 47, was allegedly caught speeding while off duty on the A171 near Guisborough, in July last year. It was claimed he was travelling at 58mph in a 50mph zone when he was recorded by a mobile speed camera unit. A month earlier, PC McFarlane, 35, an officer for 14 years, was allegedly caught on the same stretch of road doing 60mph while driving an unmarked police car.

Both men received notification of the alleged offences from Cleveland Police and each faced a fixed penalty fine of £60 and three points on their licences. But they consulted an expert in traffic signs who told them some of the signs warning drivers of the speeding crackdown in the area were illegal.

The separate speeding fines against the officers were dropped on Tuesday when the Crown Prosecution Service offered no evidence at Guisborough Magistrates' Court. Cleveland Police acting Assistant Chief Constable John Burke later said the case had been dropped with the utmost reluctance.

A spokesman for Redcar and Cleveland Borough Council, which is responsible for the signs, said: "We are expecting to start work on replacing all the 16 signs which are considered to be non-prescribed in the very near future."

On Wednesday, it emerged that the day after being caught doing 58mph on the A171 near Guisborough, PC Burlingham was caught driving at 78mph on the same road. As this is above the national speed limit, it is an offence no matter what signs are on the roadside.

But the Crown Prosecution Service was unable to prosecute because more than six months had elapsed since the alleged offence on July 21 last year.