Thousands of motoring offences could be thrown out following an appeal court decision by Scotland's most senior judge.

A test case found that legislation which forces the owner of a car to reveal who was driving was a breach of the right to silence.

The ruling, by the Lord Justice General, Lord Rodger, sitting with Lord Marnoch and Lord Allanbridge, could throw the legal system into disarray and make it impossible for the Crown to prosecute many motoring offenders.

At present, police have the power to force car owners to disclose who was driving their vehicle at the time of an offence.

Section 172 of the Road Traffic Act makes it an offence for the owner to refuse to divulge the information.

However, Lord Rodger found that this was a breach of a suspect's right to silence under the European Convention on Human Rights.

The ruling came to light following a test case brought to the appeal court in Edinburgh by lawyers acting for Margaret Brown who was charged with drink driving.

Police were called to attend an incident at an Asda superstore in Dunfermline, in Fife, last year.

Travelled by car

They approached Miss Brown and noticed that her breath smelt of alcohol. When they asked how she came to be at the store she said she travelled by car.

Miss Brown said a car in the car park was her vehicle and when they checked her handbag they found a set of car keys.

Officers used their powers under Section 172 of the Road Traffic Act to compel her to indicate who was driving the vehicle and she told them it was her.

Without using the section the police could not compel her to tell them who was driving the car.

Miss Brown, 30, of Glen Nevis Drive, was charged with drink driving and the theft of a bottle of gin from the store.

A sheriff at Dunfermline Sheriff Court rejected a legal challenge raised by her agent and her lawyers then turned to the appeal court to challenge the use of the evidence obtained.

They argued that as she was compelled to give an answer it would infringe her right to a fair trial if the Crown was allowed to rely on it as a significant part of the case against her.

They said that if the admission was used by the procurator fiscal to prosecute her it would be incompatible with the European Convention rights of a suspect to remain silent.

Effective prosecution

The Solicitor General, Colin Boyd, QC, had argued against the appeal and said there was a "general need" for a provision such as Section 172 for the effective prosecution of road traffic offences.

But Lord Rodger said: "I am satisfied that the appellant was subject to compulsion to make an incriminating reply under threat of being found guilty of an offence and punished with a fine."

The senior judge said the use the Crown planned to make of her answer to police "would offend her right not to incriminate herself" which was a key element in Article 6(1) of the European Convention.

The solicitor general warned the court that such a ruling would have "momentous effects" on the use of roadside speed cameras and damage the chances of successfully prosecuting many hit-and-run cases.

The Crown Office said senior counsel was studying the ruling, but that they would be seeking leave to appeal to the Privy Council.

The court system was turned on its head in November when it was ruled that, under the European Convention, people appearing before temporary sheriffs could not be guaranteed an independent and impartial tribunal.