What is m15?

MI5's performance in running a stable of double agents during the Second World War. MI5 was able to acquire clues to the existence of other Abwehr spies, and provide doctored documentation for future arrivals. Each individual was assigned a case officer from a specialist section within the counter-espionage branch to monitor every aspect of the agents' handling. A small inter-agency committee was created to liaise with other interested departments, especially to cope with the thorny issue of precisely what information could safely be conveyed to the enemy. "MI5 established a secret detection centre at Ham Common in which suspects could be isolated and interrogated."