Detention centres were buildings set up by the military to house criminals while martial law was in effect during Operation Golden Age. Inmates were held until the end of the crisis.
The Third Doctor and Sarah Jane Smith were being transported to a detention centre, having been found guilty of looting, when a tyrannosaur appeared. The soldiers accompanying them left the vehicle to fend it off allowing the Doctor and Sarah to escape and run away. (TV: Invasion of the Dinosaurs)