GARDAÍ could be facing a raft of legal challenges after revaluing some drugs at more than six times their previous street price.

A potentially embarrassing loophole was highlighted in a circuit-court case last week when a drugs mule was found not guilty of one criminal charge because detectives involved in the case had put too high a value on the drugs involved.

A 25-year-old Englishman, who was arrested after carrying drugs into Dublin Airport, was found not guilty of importing more than €13,000 worth of cannabis into the country.

Had he been found guilty of the charge, he would have faced a mandatory 10-year prison sentence.

His legal advisers, the Dublin solicitors firm of AC Pendred, had successfully argued that the original valuation by gardaí of drugs worth €45,925 was too high.

Dozens of legal challenges are now possible following the Sunday Tribune's revelations earlier this month that gardaí had begun putting higher values on certain drugs.

It is understood that gardaí had been quoting a per-gram value of €9 for cannabis herb during the case.

However, the man's legal team argued that a valuation of €2 per gram – or €10,205 in total – was fairer based on a garda circular from 2004 and information supplied by the Department of Justice.

The man at the centre of the case had already pleaded guilty to the lesser charge of unlawful possession of drugs but was found not guilty of the more serious charge.

Lawyers believe the case has exposed a potential flaw in drugs legislation, which relies on monetary values instead of the actual weight of drug involved.

One solicitor said: "The difference between possession of €10,000 worth of drugs and €13,000 worth of drugs might seem tiny but it can be enormous when it comes to sentencing.

"A person caught with the higher value faces a mandatory 10-year sentence. The problem is that the legislation relies on garda valuations of what constitutes €13,000 worth of drugs and that is something that isn't consistent."

Gardaí have recently undertaken a review of all drug prices in order to better reflect the actual value of illegal substances on the street.

As part of that review, the price of cannabis herb was upgraded from just €2 per gram to €12 per gram and the estimated price of cocaine is also likely to rise.

Gardaí would not comment on the case saying: "We are not in a position to provide a comment on an individual case."