A vital part of any policing system is having robust mechanisms to deal with allegations of wrongdoing against officers.

Police men and woman possess powers ordinary citizens do not and the public should know that abuses are dealt with firmly.

Police Scotland’s Counter Corruption Unit (CCU) was established in 2013 and was supposed to blaze a trail for ethical standards in policing.

Sir Stephen House, at that time the chief constable, put his name to the press release announcing the new Unit’s creation: "The actions of the few who engage in corrupt activity have a disproportionate impact on public confidence and the reputation of any public organisation. At a time of increasing budget constraints on the public purse, it's important we do all we can to protect the public sector and our communities."

Kenny MacAskill, who was subsequently accused of keeping House on too long a leash, also joined in: "It is crucial that the ethos of prevention is very much at the core of the unit to ensure the early detection of criminality and minimise the harm it can inflict."

However, the CCU has now become a badge of shame for a single force that is beginning to see improvements in other aspects of its performance.

The Unit’s key failure is well known and does not require an extensive re-telling.

Although the CCU was set up to root out corrupt officers, the Unit unlawfully used its spying powers in a bid to find out whether retired and serving officers had leaked information to the media.

This reckless action has set in train various inquiries, the most important of which is the “assurance review” being undertaken by Her Majesty’s Inspectorate of Constabulary in Scotland (HMICS).

However, the review is wider than the spy scandal and is examining the operations and procedures of the CCU in recent years.

On this front, the Unit stands accused of mis-treating officers by subjecting them to unwarranted and disproportionate treatment.

As we reveal today, eleven officers met the HMICS last week to talk about their experiences of being under investigation by the Unit.

One officer described the CCU as being like the “Gestapo”, while colleagues recounted horrendous stories about their alleged treatment.

These stories, which build on other claims heard by this newspaper, paint a picture of a Unit that has been a law unto itself.

The CCU must be abolished and its powers given to a new body that is not tainted with the failures of the past.