A KEY plank of Police Scotland's stop and search policy is under increasing pressure after it emerged that officers had delivered a failure rate of 84%.
So-called "suspicionless" searches are in some areas of the country finding illicit items in only one in 10 operations.
In its first year, the single police force recorded more than 600,000 frisks, proportionately far higher than any other part of the UK and nine times the level of the New York Police Department.
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Officers can either undertake searches on individuals on a statutory basis, which requires reasonable suspicion, or carry out non-statutory frisks, which have no legal authority. Suspicionless searches, ruled out for police south of the Border, accounted for around 70% of all recorded searches in Scotland last year.
New figures showing the success rate of non-statutory searches in the first nine months of 2013 - defined as the detection of knives, drugs and other items - have cast doubt on the policy's effectiveness.
Of the 142,992 searches recorded in G division, which covers Greater Glasgow, 70.9% were suspicionless. Of these frisks, only 15.9% were positive.
In U division, which spans Ayrshire, 16% of the 72,460 non-statutory searches found something. In Edinburgh's E division, the detection rate for suspicionless frisks was 12.9%, while the figure in Lothians and Scottish Borders was 13.4%.
The lowest rate was in the Highlands and Islands, or N Division, which recorded an 11.6% return.
The high failure rates come in spite of senior officers insisting that searches are based on police intelligence.
In January, assistant chief constable Wayne Mawson said: "Searches are targeted and intelligence-led and often conducted with the consent of those involved."
A recent review by the Scottish Police Authority, which scrutinises the single force, found that frisking was a "useful" tactic, but concluded that the "extent to which stop and search contributes to falling violence is not clear".
Suspicionless searches have now become a political issue, with the Liberal Democrats calling for the abolition of the practice. The party is to lodge amendments to criminal justice legislation requiring that all searches are based on reasonable suspicion.
Alison McInnes, the Scottish Liberal Democrat justice spokesperson, said: "The evidence does not match the claims over non-statutory stop and search. Is simply casting the net wide in hope of an eventual catch the best use of police time or the best deal for protecting civil liberties?"
Professor Alan Miller, chairman of the Scottish Human Rights Commission, said: "These powers can be used even where there is no reasonable suspicion of the person being stopped. This risks searches being carried out without informed or freely given consent by those being stopped. Increased use of this kind of stop and search can also have a worryingly adverse impact on relations between the police and communities."
Mawson said: "Through the intelligent use of stop and search ... Police Scotland aims to ensure we can bring an improvement to a community affected by crime and keep people safe.
"To ensure this, we consider all information available, including where, when and what types of crimes and incidents have been reported in an area along with all other information from those living and working in that community. Only by understanding the issues which need to be addressed can we consider the best way to direct our resources and ensure that any tactics we use will keep people safe."