MI6

The service derived from the Secret Service Bureau, which was founded on 1 October 1909. Its first director was Captain Sir Mansfield George Smith-Cumming, who often dropped the Smith in routine communication. He typically signed correspondence with his initial C in green ink. This usage evolved as a code name, and has been adhered to by all subsequent directors of SIS when signing documents to retain anonymity.

The main mission of SIS is to collect foreign intelligence for the United Kingdom. It provides the British government with vital intelligence regarding foreign events and informs concerning global covert capabilities to uphold national interests, security and protect the country's economic well-being. SIS works with the Foreign, Commonwealth & Development Office and therefore falls under the supervision of the Foreign Secretary. SIS officers and agents engage in operations and missions all around the world. The SIS regularly cooperates and works with MI5 and GCHQ regarding domestic and cyber intelligence. SIS has three primary tasks:

MI6 is nicknamed The Circus. Some say this was coined by John le Carré (former SIS officer David Cornwell) in his espionage novels and named after a fictional building on Cambridge Circus. (In le Carré's universe, "The Circus", the highest command body of the agency, is a metonym for the agency itself.) Leo Marks explains in his World War II memoir Between Silk and Cyanide that the name arose because a section of the Special Operations Executive (SOE) was housed in a building at 1 Dorset Square, London, which had formerly belonged to the directors of Bertram Mills circus.