Keeping watch on a suspect. The Police Act 1997 and the Regulation of Investigatory Powers Act 2000 provide a formal system for authorization of intrusive surveillance operations by chief police officers. A team of independent commissioners oversees the arrangements and investigates complaints. Police and customs officials are also required to seek prior approval from a commissioner for authorizations in particularly sensitive cases – such as those involving legal privilege, for example – except in cases of emergency. See also electronic surveillance.