Excuses for Police Scotland have worn thin. Arguably, even the ever-growing list of its controversies is already tantamount to a scandal. Where there is no ambiguity, when what is at issue is a flouting of parliamentary will, the word controversy will no longer do.

On February 4, the then Interception of Communications Commissioner, Sir Anthony May, published his “Journalist Inquiry Report” into allegations police had misused their powers under Chapter 2 of Part 1 of the Regulation of Investigatory Powers Act (RIPA). On March 25, a new code of practice duly came into force.

This was intended explicitly to ensure “law enforcement acquisition of communications data to determine journalistic sources” would require a judge’s authorisation. No ifs or buts. Sir Anthony had established police were sometimes exceeding their authority flagrantly. The principle affirmed was that protection of a journalist’s sources is overwhelmingly in the public interest.

In July, the Interception of Communication Commissioner’s Office (IOCCO) let it be known that two forces had decided to dispense with such fripperies. Our sister paper, the Sunday Herald, then established that Police Scotland was one of the two.

With Sir Anthony stepping down, silence descended until his successor could be named.

The world did not come to a halt. Indeed, Neil Richardson, deputy chief constable with responsibility for Police Scotland’s Counter-Corruption Unit (CCU), became one of three candidates in the contest to replace Sir Stephen House as chief constable. This might count as an unfortunate coincidence for the force, given the CCU was responsible for “serious” breaches of the code of practice.

The code of practice states the “senior responsible officer” must ensure compliance with RIPA, ensure “the integrity of the process”, and see that “errors” are reported to IOCCO while taking steps to prevent any repetition.

Anyone struggling to understand why this matters should recall the assurances from various governments as powers of data surveillance have been acquired. We have been told sophisticated threats require sophisticated responses. We have been assured – promised, indeed – that officialdom’s sole concern is with crime and terrorism.

The Police Scotland case makes a mockery of such vows. It causes a deep, rational suspicion when still more demands for more powers are made. The victory for Theresa May, the Home Secretary, in securing Labour and Liberal Democrat support for her draft data surveillance bill palls when we consider what has gone on.

Step by step, the state is becoming more intrusive. The lines of separation between the realms of public and private are being eroded. If nothing else, Police Scotland’s high-handed treatment of journalism should make anyone contemplating official regulation of the press think twice.

“Who will guard the guards?” asked the Roman poet. A better question for today: Who will trust the guards?