Gary Brown was found guilty of drink driving

During the five-day hearing, the court heard how police breath-tested Mr Brown on 2 January, 2000 after they found his G registration Vauxhall Nova on its side in Falkirk's New Hallglen Road.

He gave two samples on the Intoximeter which indicated that he was over the drink-drive limit.

Mr Brown's QC, Neil Murray, attempted to have the case thrown out by challenging the legality and validity of the breath-test machine.

He told the court: "We are supposed to be talking here about a scientific instrument.

"What we have is an elastic ruler - it's not much use."

Mr Murray argued that the Intoximeter was unreliable as it could not tell the difference between breath alcohol and mouth alcohol.

Varying results

The advocate also alleged that the machine was unlawful because it had not been made by US firm Intoximeter Inc of St Louis, Missouri.

He said this contravened an order signed by the secretary of state for Scotland when he authorised the machines use in 1998.

Dr John Mundy, a former Home Office scientist, told how he and a colleague, Professor Hugh Makin, tested the Intoximeter at Falkirk Police Station last month.

The legality of the breathalyser was challenged

He said the machine gave positive results on several occasions even though they had both swilled their mouths with a small mixture of alcohol and water.

Dr Mundy said he had tested more than 90 Intoximeters throughout Britain and found varying results in their capacity to distinguish mouth alcohol and breath alcohol.

Defence advocate Mr Murray said the machine was required to measure alcohol in the breath accurately but said the evidence given by Dr Mundy showed this "is not happening".

But the evidence from both scientists was described as "irrelevant" by depute fiscal Alastair Carmichael.

He said: "In real life, a person is not going to be allowed to swill alcohol around in his mouth before being tested."

Lawful and reliable

Mr Carmichael argued that any failure by the machine to detect mouth alcohol "did not deflect from its ability to detect deep lung alcohol".

He also said that Intoximeter Inc at one time did "manufacture" the device and that having helped design the equipment was part of the manufacturing process.

Martin Morrow: "Complex issue"

Sheriff Caldwell ruled "The identity of the manufacturer lends nothing to the specification and is therefore not a necessary element in the type approval order."

He found that the machine was reliable and he dismissed the tests carried out by Dr Mundy and Prof Makin, saying their test conditions would never arise "in actual use".

But Mr Brown's defence team said they would appeal the ruling that the Intoxomiter was lawful and reliable.

His solicitor, Martin Morrow, said: "The case is a complex issue but the fundamental issues require to be resolved in the High Court for the benefit of all the citizens of Scotland."

It was thought that a victory for Mr Brown could have thrown the breath-testing system throughout Scotland into chaos.