The Scottish Police Authority (SPA) failed to progress eight misconduct complaints against senior officers, a report has found.

The Police Investigations and Review Commissioner (PIRC) carried out a review of the SPA's complaints handling procedures between April 2015 and March 2017.

The commissioner, Kate Frame, said she found a number of deficiencies in the oversight body's process for dealing with complaints against Police Scotland officers and its own staff.

The audit, released on Friday, said the SPA received 14 complaints about senior officers which should have been progressed as misconduct allegations.

In eight of these cases, the SPA's complaints department did not carry out enough enquiries to establish the details of the allegations.

In another category of allegations against senior officers, known as "relevant complaints", there was no evidence the SPA carried out sufficient enquiries in the majority of cases.

The PIRC audit also found the average time taken to conclude handling misconduct allegations was 210 days.

Ms Frame said: "The audit has highlighted a number of deficiencies within the SPA's current complaint handling practices.

"Decisions on complaints were made which lacked clarity and transparency, and in many cases there was insufficient explanation to demonstrate how the decision was reached.

"The average time taken by the SPA to conclude complaints and preliminary misconduct assessments was excessive and disproportionate, as was the emphasis placed on members of the public by the SPA to produce evidence in support of their complaint.

"To provide greater clarity for SPA staff on how complaints should be assessed and handled, I recommend that the SPA's internal guidance should be revised."

Susan Deacon, chairwoman of the Scottish Police Authority, said: "This latest PIRC report raises a number of important areas for the SPA's attention, some of which have already been dealt with or are in progress.

"Going forward, I believe it is essential that the SPA work together with other organisations with a role and interest in complaint handling, to ensure that our systems and practices are robust and work effectively to maintain public confidence and trust in policing."