The department is headed by Superintendent Ted Hastings, who has been in charge of the unit since Series 1. Its responsibility is to investigate members of Central Police who are suspected of being involved in corruption, misconduct or mishandling of case evidence.
Its offices are located in the AC-12 Building, a large police station in the Kingsgate area of the city which shares operational duties with some other departments. Its sister agency is AC-9, a separate and smaller professional standards department which also carries out Witness Protection duties.
In cases where officers from other Professional Standards departments within neighbouring forces (such as the East Midlands Constabulary's AC-3) are accused of wrongdoing, the unit can be requested to investigate as an independent outside organisation.
The department has a negative reputation amongst the majority of officers within Central Police, who believe the unit places too much focus on investigating fellow police officers (often over trivial matters) instead of catching "real" criminals. In Series 4 it is mentioned by DCI Roz Huntley that the department scores below the national average in their promotion of female officers to high ranking positions.
Given immunity from prosecution for sexual activity with a child in exchange for providing information into Vice Squad corruption. The Crown Prosecution Service has yet to determine which charges he will face.