STEPHEN House's former force produced a league table of officers conducting stop searches and explicitly linked an increase in frisks to getting a promotion.

Strathclyde Police warned that the volume of searches carried out by individual officers would be considered when they wanted to apply for a special diploma needed to move through the ranks.

House's frisk policy has unravelled amid a series of controversies, including whether individual officers in Police Scotland have been set targets to step up the number of frisks.

Giving evidence to MSPs recently, House said there are "no targets for volume of stop and search", but conceded there may be a "perception" of officers feeling under pressure.

Calum Steele, the Scottish Police Federation general secretary who sat next to House during the Holyrood session, insisted his members felt there were targets.

However, a leaked email from the Strathclyde force in early 2013, weeks before Police Scotland went live, reveals how a targets culture was used to pressurise officers into pursuing House's signature policy.

The email, sent from an area commander to managers, noted that search levels were down compared with the previous year.

The senior police officer, who wrote that the chief constable had commented on the area's poor performance, also produced a league table of searches.

He claimed that all officers who did not carry out enough frisks would have a key performance indicator - effectively a target - included in their personal review.

The area commander also stated that the volume of searches, coupled with other performance data, would be used when considering applications for specialist posts, transfers and the police Diploma.

According to a report by the Scottish Centre for Crime and Justice Research, Strathclyde set a target in 2012/13 of officers carrying out 459,438 frisks.

This was an 89% increase on the target for 2009/10.

At the time of the email, Campbell Corrigan was acting chief constable of Strathclyde, as House was preparing for Police Scotland to become operational.

Scottish Tory justice spokeswoman Margaret Mitchell MSP said: "Within Police Scotland there have been different accounts about performance targets set for stop and search, and how it's been deployed.

"What is not in doubt, as a result of this email being unearthed, is that ... the old Strathclyde force ... not only used targets but also performance indicators, where targets were linked to promotion. And this is deeply worrying."

Scottish Liberal Democrat justice spokesperson Alison McInnes MSP said: "Police Scotland regularly denies that there have ever been any targets for the volume of stop and search conducted, despite claims to the contrary from frontline officers and staff representatives.

"League tables and key performance indicators are targets in all but name if they are used to coerce officers into conducting searches.

A spokesman for Police Scotland said: "Police Scotland is on record as stating the culture which exists in the single service around the practice of stop and search is demonstrably different to that which existed in legacy forces. Since Police Scotland came into being in April 2013, no targets have been set for volume stop and searches and it is not linked in any way to promotion or advancement."