A sheriff provoked outrage last night after letting off a policeman who drove while more than twice the limit.

Sheriff Sandy Eccles made the judgment despite admitting the officer's excuse was ''extraordinary''.

Detective Constable Lee Hughes, 52, of Northcott, Bracknell, Berkshire, claimed he had to drive because his girlfriend ''freaked out'' in thick fog.

Road safety campaigners last night condemned the judgment as bizarre and hard to understand.

Ms Isobel Brydie of the Scottish Campaign against Irresponsible Drivers (SCID) called for an inquiry.

She said: ''I find this an extremely strange decision and one that could open the floodgates for others.''

Mr Hughes told Perth Sheriff Court he had taken over at the wheel to drive the car off the motorway.

Depute fiscal Chris Macintosh described his story as ''totally absurd and demonstrably false''.

But Sheriff Eccles said the catalogue of events was so extraordinary he could believe them.

The court heard how Mr Hughes, 29, and Miss Rebecca Burgess, 27, had gone to Dunkeld, Perthshire, to attend a friend's wedding.

Mr Hughes said they were then thrown out of the hotel by the manager for late-night rowdiness.

They walked off to another hotel but could not get in there, so the couple then decided to drive their hired car to Perth.

Miss Burgess, a journalist, told the court she had driven because she had less to drink than Mr Hughes.

The couple got to Perth but could not find a hotel open, Mr Hughes said.

They then decided to drive back to Edinburgh Airport, where they had picked the car up.

As Miss Burgess drove down the motorway from Perth, thick fog began to descend which caused her to panic.

Miss Burgess said she started crying and finally stopped the car at the side of the road. She said Mr Hughes told her she had to go on, because she couldn't stop where she had.

Mr Hughes then took over driving. she said: ''He wasn't driving very long when he told me there was a sign for services and he was pulling off.''

A passing patrol car approached Mr Hughes' car when he was parked at a service station in Kinross. Officers discovered he was over twice the drink-drive limit.

Mr Hughes made no mention of being forced to drive the car to safety when he was arrested.

Mr Macintosh said a compulsion defence could apply where a drink driver was in ''immediate danger or fear of bodily harm''.

He added: ''I would ask the court to disbelieve the accused and his witness. Their story is palpably absurd and demonstrably false.''

He said they would have been safer to stay parked on the hard shoulder, and as a police officer he should have known to say something when stopped.

Sheriff Eccles, however, accepted Mr Hughes' plea of not guilty on the basis that he had to act as a matter of compulsion.

The judgment was slammed by Ms Brydie, who said: ''Are there one set of rules for some people and a different set for others. The sheriff is setting a precedent that you can get off with an excuse like this. That's very strange and worrying.''