The body responsible for oversight of police has been ordered to review complaints made about Scotland's two most senior officers.

Allegations concerning negligence with information were made against Chief Constable Phil Gormley and former deputy chief constable Neil Richardson.

Neither complaint was upheld by the Scottish Police Authority (SPA), but the Police Investigations & Review Commissioner (Pirc) has found the body did not handle the allegations reasonably.

The commissioner has now ordered the SPA to review its decisions and apologise to the man involved.

It comes as Mr Gormley is separately being investigated for alleged gross misconduct.

A spokesman for the SPA said: "We note the outcome of the Pirc's complaint handling review.

"A reconsideration of the relevant complaints will be initiated as soon as possible and we will work closely with the Pirc to address the learning points highlighted within the report."

The complaints came from a man who sent a letter to Mr Richardson in November 2015 raising concerns about officers in the Professional Standards Department (PSD).

This was passed to a superintendent in charge of the same department, who replied in December that year.

The man then wrote to the chief constable complaining about this.

An inspector of Mr Gormley's secretariat wrote back saying his letter had been passed to Mr Richardson - the officer the man had complained about.

In March 2016, it was alleged to the SPA that the passing of these letters to the person or department they were about was negligent, but the body did not uphold his complaints.

The subsequent Pirc review found the body did not adhere to protocol when handling the complaint against Mr Richardson.

It found there was no reasoning in SPA responses as to why it decided the allegation would not, if proved, amount to misconduct.

There was no explanation of what inquiries were carried out, what facts were established, or how these facts led to the complaint not being upheld.

It was deemed by the commissioner that the inquiry into the complaint was insufficient and the response inadequate.

Meanwhile, the Pirc review said it was not acceptable for a letter of complaint about a police officer to be passed to that same individual.

As the complaint was about a senior officer, it should have been sent to the SPA.

The report said the commissioner would be contacting Mr Gormley and his secretariat to make this clear.

The SPA has been told to send a fresh response to the man addressing the issues raised and fully explain the outcome of the reconsiderations.

After the appointment of deputy chief constable Iain Livingstone in May 2016, a review of the PSD was ordered.

It resulted in a new National Gateway unit being established, which assesses all potential complaints that can be dealt with by the PSD, the anti-corruption unit, local policing divisions and other departments.

Mr Livingstone also reviewed executive support functions over complaints being made against the senior officers and how they were processed.

He added: "Robust handling procedures are now in place in relation to complaints against chief officers which ensure relevant matters are directed to the SPA and PSD.

"I believe these changes will now address the issues relating to Police Scotland identified in the Pirc report."