SINCE the formation of a single police service in Scotland four years ago it was universally acknowledged there needed to be a powerful system in place to independently probe the actions of police officers.

Before the watchdog's creation in 2013, the eight individual police forces investigated each other.

The Hamilton-based Police Investigations and Review Commissioner (PIRC) was set in recognition that they could not rely on officers being brought in from an outside area to investigate complaints.

Over the past four years it has been looking into a series of police scandals leading to it becoming one of Scotland's most overworked quangos.

With the number of complaints being investigated having shot up there is continuing concern about whether PIRC and its 59 staff can manage with the growing workload.

Its official role is to "is to undertake independent investigations into the most serious incidents involving the police and to provide independent scrutiny of the way police bodies operating in Scotland respond to complaints from the public".

The office of the Commissioner decides whether to investigate complaints against Police Scotland, and carries out investigations into these, and other incidents including deaths or serious injuries suffered while in police custody and similar incidents following police contact. Some of their more serious cases are referred to it by the Crown.

Thenon-departmental public body of the Scottish Government is also responsible for investigating complaints by members of the public against the Scottish operations of the National Crime Agency, British Transport Police, Civil Nuclear Constabulary, Ministry of Defence Police, and HM Revenue and Customs.

The Commissioner must investigate any allegation if directed to do so by the Crown Office where there is an indication that a person serving with the police may have committed an offence or if the circumstances of any death involves a police officer which the Procurator Fiscal is required to investigate under the Fatal Accidents and Sudden Deaths Inquiry (Scotland) Act 1976.

PIRC must also investigate any allegation of misconduct referred by the SPA, if the Commissioner assesses that the matter, if proved, would amount to gross misconduct.

The Chief Constable must refer to the Commissioner any death or serious injury to somone where a direct or indirect contact with the police may have caused or contributed to it. He must also refer any police use of a firearm, taser or CS spray.

The Scottish Police Authority has to refer cases of potential misconduct by a senior officer if it considers that the matter needs to be investigatedIRC investigators have the powers and PIRC has the powers of a police constable when investigating on behalf of the Commissioner and includes powers to detain, arrest, question, report for prosecution, seize productions, including firearms, drugs and any other materials or documents.

Investigators, acting on behalf of the Commissioner, can enter any premises used by the Scottish Police Authority or Police Scotland and search and seize any relevant material.