--- aliases: - Secret Intelligence Service - SIS category: Intelligence & Government created: 2026-05-14 location: London, United Kingdom relations: - end: 1961 fn: 5 reverse: true type: employed_by with: '[[George Blake]]' summary: The United Kingdom's foreign intelligence service, put on a statutory footing in 1994, which ran the 1953 Iran coup with the CIA and employed the Soviet agent George Blake until 1961. tags: - Organization - UnitedKingdom - Intelligence - MI6 - SIS - ColdWar updated: 2026-09-22 --- The Secret Intelligence Service (SIS), known popularly as MI6, is the [United Kingdom](/places/united-kingdom/)'s foreign intelligence service, responsible for collecting intelligence from overseas sources. It operates under the authority of the Foreign, Commonwealth and Development Office and reports to the Foreign Secretary, with parliamentary oversight through the Intelligence and Security Committee. The Intelligence Services Act 1994 provides that "there shall continue to be a Secret Intelligence Service" under the authority of the Secretary of State, with the functions of obtaining and providing information "relating to the actions or intentions of persons outside the British Islands" and performing "other tasks" relating to them, in the interests of national security, of "the economic well-being of the United Kingdom," or of the prevention or detection of serious crime.[^1] Its current headquarters, known as Vauxhall Cross, opened on the south bank of the Thames in [London](/places/london/) in 1994; the building's distinctive architecture made it a publicly known landmark, ending decades of official non-acknowledgment of SIS's existence.[^2] ### Origins and World War II In July 1909, amid public alarm over German espionage, the Committee of Imperial Defence under Prime Minister Herbert Asquith established a Secret Service Bureau, which was split into Home and Foreign Sections, the forerunners of [MI5](/organizations/mi5/) and SIS; the Foreign Section was given to Mansfield Cumming, a 50-year-old Royal Navy officer with neither intelligence experience nor languages, the original "C." Cumming set up in Ashley Mansions, Vauxhall Bridge Road, and early in 1910 registered a cover address with the Post Office as "Messrs Rasen, Falcon Limited," shippers and exporters. Dick White, Director General of MI5 from 1953, was moved by Prime Minister [Anthony Eden](/people/anthony-eden/) to head SIS in 1956, the only man to have led both services, and remained until 1968; in 1964 he oversaw the Service's move from Broadway Buildings to Century House in Lambeth.[^3] During [World War II](/events/world-war-ii/), SIS worked alongside the Special Operations Executive (SOE) and the American [Office of Strategic Services](/organizations/office-of-strategic-services/), forming the intelligence relationships - particularly with the United States - that became the post-war [Five Eyes](/organizations/five-eyes/) intelligence alliance. The [UKUSA Agreement](/programs/ukusa-agreement/) of 1946 formalized intelligence sharing between SIS's signals partner [GCHQ](/organizations/gchq/) and the American [National Security Agency](/organizations/nsa/).[^2] ### Operation Boot: The Iran Coup SIS's most historically significant joint operation with the [Central Intelligence Agency](/organizations/central-intelligence-agency/) was Operation Boot (the American component was called Operation Ajax) in August 1953. British and American intelligence officers, including SIS officer Norman Darbyshire and CIA officer Kermit Roosevelt Jr., organized a coup in [Iran](/places/iran/) that removed elected Prime Minister Mohammad Mosaddegh and restored [Shah Mohammad Reza Pahlavi](/people/mohammad-reza-pahlavi/) to full power. The British motivation was primarily the recovery of nationalized Anglo-Iranian Oil Company assets; the American motivation was preventing a communist takeover. The operation established the template for Cold War covert regime change and the long-term relationship between the CIA and [SAVAK](/organizations/savak/), the Shah's intelligence service.[^4] ### Cold War Operations SIS maintained liaison relationships with intelligence services across the [Middle East](/places/middle-east/), Africa, and Asia throughout the Cold War. Its cooperation with Mossad - the [Israeli](/places/israel/) intelligence service - is described in numerous memoirs and investigative accounts as extensive, covering operations in Arab states, Iranian intelligence assessments, and personnel exchanges. [David Kimche](/people/david-kimche/), the senior Mossad officer who initiated the Iran-Contra arms channel, was born in London and cultivated SIS relationships throughout his career. In [Afghanistan](/places/afghanistan/), SIS coordinated with the CIA's Operation Cyclone through SAS training programs for mujahideen fighters during the Soviet occupation (1979-1989). The relationship between SIS and Pakistan's ISI during this period was close and operationally significant.[^2] [George Blake](/people/george-blake/), an SIS officer who had worked for the KGB, was exposed in 1961 on information from the Polish defector Michał Goleniewski, confessed when confronted in April 1961, and was tried at the [Old Bailey](/organizations/old-bailey/) and sentenced to 42 years.[^5] ### Robert Maxwell Multiple former intelligence officers, including [Ari Ben-Menashe](/people/ari-ben-menashe/) and Victor Ostrovsky, asserted that press baron [Robert Maxwell](/people/robert-maxwell/) worked simultaneously for [Mossad](/organizations/mossad/) and had relationships with multiple Western intelligence services including SIS. Maxwell's access to senior British politicians, his publishing empire (which included scientific journals widely distributed in the Soviet bloc), and his Central European connections made him valuable to intelligence services. [Nicholas Davies](/people/nicholas-davies/), his [Daily Mirror](/organizations/daily-mirror/) foreign editor, was accused of operating as a Mossad asset. SIS's relationship with Maxwell was not officially confirmed.[^4] [^1]: Intelligence Services Act 1994, c. 13, s. 1. https://www.legislation.gov.uk/ukpga/1994/13/section/1 [^2]: "Secret Intelligence Service (SIS/MI6)," UK Government. https://www.gov.uk/government/organisations/secret-intelligence-service [^3]: Secret Intelligence Service, "Our History," archived January 23, 2023. http://web.archive.org/web/20230123001042/https://www.sis.gov.uk/our-history.html [^4]: Dorril, Stephen. *MI6: Inside the Covert World of Her Majesty's Secret Intelligence Service.* Free Press, 2000. [^5]: Weiner, Tim. *Legacy of Ashes: The History of the CIA.* Doubleday, 2007; Murphy, David E., Sergei A. Kondrashev, and George Bailey. *Battleground Berlin: CIA vs. KGB in the Cold War.* Yale University Press, 1997.