SCOTLAND's human rights tsar has called for one of Police Scotland's flagship crime policies to be scrapped due to "serious concerns" about its legality.

Professor Alan Miller said 'suspicionless' stop and search operations, which make up over two thirds of all frisks, would "likely" be defeated if challenged in court and could trigger "emergency" measures at Holyrood.

Intended to find guns, knives and drugs, stop and search was deployed on an industrial scale by Strathclyde Police and rolled out nationally by single force chief constable Stephen House.

Over 600,000 searches were carried out in 2013/14, a frisk rate that is proportionately nine times higher than the area covered by the New York Police Department.

Around 30% of the single force's searches were 'statutory' - meaning they were based on officers having a reasonable suspicion of an individual possessing questionable items.

However, the remaining 70% were non-statutory, meaning they were suspicionless and not rooted in law.

These so-called "consensual" searches were outlawed in England and Wales, and have been used on young children.

Miller, who was elected as the Scottish Human Rights Commission chair in 2007 and re-nominated in 2013, criticised the practice saying: "When used appropriately, statutory stop and search can help to keep us all safe. However, the Commission has serious concerns about the legality and scale of non-statutory stop and search of individuals. These searches can be conducted without any reasonable suspicion of a crime being committed or any concern over risk to public safety."

He said searches must be encoded in law and called for suspicionless frisks to end: "The Commission believes that proactive steps should be taken now to strengthen the legal framework within which any and all stop and searches take place. There should be no non-statutory stop and search. This is already the case in England and Wales, where the practice was ended some considerable time ago."

Failure to end non-statutory searches, he said, could end up in the courts: "Current police practice is open to legal challenge." He added that it is "likely" that "such a challenge [would] be successful".

In 2010, the UK Supreme Court ruled that the way suspects were detained in Scotland was incompatible with human rights law, a decision that triggered immediate Holyrood legislation.

Miller believes suspicionless searches may breach Article 8 of the European Convention on Human Rights, which covers the right to a private life.

"All of us should be free to go about our daily business and the police should only be entitled to stop and search us if they have reasonable suspicion that we are doing something unlawful," he said.

The Scottish Liberal Democrats will soon table amendments to criminal justice legislation in an attempt to stop the searches.

Party justice spokeswoman Alison McInnes said: "Scottish Liberal Democrats have always been clear that non-statutory stop and search is indefensible. Alan Miller's remarks set out clearly that the Scottish Government's ongoing support of unregulated stop and search is unfair and illiberal. We are in the process of drafting amendments and welcome Alan Miller's support for our approach to put it on a legal footing."

Dr Kath Murray, an Edinburgh University research fellow who first drew attention to the extensive use of stop and search, said: "This is an outdated policing tactic, which lacks the most basic legal safeguards. It also sits uneasily with the progressive approach to youth justice in Scotland. In the first nine months of the single service alone, over 43,000 non-statutory searches were recorded on children aged 15 and under, with a further 30,000 searches recorded on children aged 16.

"It's concerning that Police Scotland has not published detailed statistics on the use of non-statutory stop and search, and that we mostly know about the use of this tactic through Freedom of Information requests."

A Police Scotland spokesperson said: "The use of intelligent stop and search, targeted in the right place at the right time at the right people and for the right reasons, is an essential part of the policing tactics we have at our disposal to help keep our communities safe.

"Police Scotland works within the context of an ethical and legal performance framework which is robustly monitored at both command and local level as well as through regular reports to the Scottish Police Authority (SPA), via HMICS inspections and local authority scrutiny arrangements."