The B.C. Supreme Court says blowing a “warn” on an approved roadside screening device isn’t enough to justify an immediate driving prohibition — police also must have evidence of impairment.

Sitting in Kamloops, Justice Dev Dley threw out a three-day prohibition issued last year to Lee Michael Wilson, even though he admitted drinking four beers and blowing a “warn” on two separate screening devices.

Dley said the B.C. Superintendent of Motor Vehicles’ adjudicator could not rely solely on the “warn” signal — an indication of blood-alcohol content between .05 and .08 — to conclude Wilson was impaired.

He maintained that if the legislature intended the “warn” reading alone to trigger an immediate prohibition, it would have said so.

“A plain reading of the legislation requires more than just a WARN reading,” Dley insisted.

“There is no presumption that a driver’s ability to drive is affected by alcohol solely on the basis of a WARN reading. Unless Mr. Wilson’s ability to drive was affected by alcohol, the peace officer had no basis upon which to issue the Notice.”

A leading critic of the roadside-prohibition scheme, Vancouver lawyer Paul Doroshenko said the ruling will have widespread effects.

“Taxpayers are going to be picking up a lot of towing and storage charges for a lot of people,” he said.

“This decision applies to 90-day suspensions, too. ... What’s happened is this imports all the criminal law with respect to reasonable and probable grounds that the superintendent’s office would never even consider: They said that’s criminal law and we don’t have to consider it (in an administrative process) … Now, issuing a prohibition requires reasonable and probable grounds.”

He said the superintendent’s office assumed “everyone (who blew a ‘fail’ or a ‘warn’) was guilty” and therefore police didn’t need to provide evidence of impairment.

Since there is no time limit placed on appeals, Doroshenko said he expects many, many people now to ask for a review.

This is another in a series of court judgments over the last year that raise concerns about sections of the Motor Vehicle Act that originally came into force in 2010.

What was supposed to be a quick, cheap, administrative fix to curb impaired driving has been made far more problematic because the legislation touted as the toughest drunk-driving law in Canada was badly framed.

In December 2011, the B.C. Supreme Court ruled parts of the legislation were unconstitutional and required a re-write.

More recently, last month a Supreme Court judge pointed out there was no appeal mechanism for those accused of being impaired by drugs, and the Court of Appeal emphasized that police officers must swear or solemnly affirm their evidence.

Police have a choice of proceeding under the criminal code if a driver blows a “fail,” indicating a blood-alcohol level over .08, on a screening device or under the Motor Vehicle Act.

This ruling raises the bar considerably for police issuing immediate roadside suspensions that can cost motorists up to $5,000 in various fees and expenses — even more if increased insurance premiums and tertiary costs are included.