IT is said that Police Scotland’s Counter Corruption Unit (CCU) scares even the single force’s most experienced officers.

With bases across the country, the CCU has around 50 staff investigating corruption allegations relating to the police service and other public sector organisations.

Dubbed Scotland’s “secret" force by one critic, it was unveiled in September 2013 after the Leveson inquiry under the command of deputy chief constable Neil Richardson.

It was Richardson who referred the allegations of professional cheating made against fellow senior officer Wayne Mawson to the Scottish Police Authority.

One retired officer told The Herald that the CCU investigators are not known for their tact: “Cops are absolutely terrified of them. They pursue tiny data protection matters zealously.”

However, the CCU is supposed to uphold the law – not break it.

The Regulation of Investigatory Powers Act (RIPA) – which the CCU is supposed to comply with - provides all police forces with essential crime-fighting tools.

The RIPA allows officers to acquire the ‘who, where and when’ of communications data in the course of their criminal investigations.

In practice, this includes details of who you have called, emailed and texted, as well as location of the phone, computer or device used.

The information is routinely acquired from telecommunications firms, or places such as hotels, airports and cafes that provides digital services.

Until recently, police forces could grant in-house approval for data requests from officers during the course of their enquiries.

In 2014, the force approved 11,778 applications for communications data and turned down 282 – a rejection rate of around 2.3 per cent.

However, following allegations that forces across the UK had used the RIPA to flush out journalists’ sources, a Code of Practice governing the use of the spying law was changed.

This important change meant that any force had to obtain judicial approval before using the RIPA to determine a journalistic contact.

The problem is that the CCU ignored the new Code for protecting journalists and pushed ahead with the old system of internal approval.

The breach was uncovered earlier this year during an inspection by the Interception of Communications Commissioner’s Office (IOCCO).

First Minister Nicola Sturgeon learned of the allegations in early July and civil servants contacted the single force for confirmation, which Police Scotland provided.

Since then, Police Scotland and the Scottish Government have kept quiet in the face of repeated questioning by MSPs and journalists.

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Picture: the First Minister learned of the allegations in the summer

The force has also knocked back several freedom of information requests which have sought basic answers on whether the RIPA has been used on journalists more widely.

The fact that the watchdog has concluded that the breach has been described as "serious" by the IOCCO could also have wider ramifications for the force.

Richardson, the force’s number two, is on a shortlist of three for the chief constable’s job but is now considered an unlikely choice.

The CCU, according to force insiders, will almost certainly be overhauled.

Any probe is also likely to focus on concerns aired by MSPs that the CCU has pursued police officers over allegations that rarely make it to court.

A unit set up to root out police corruption has fallen short of its own noble purpose.