MI6

• 1. Introduction

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  MI6, formally known as the Secret Intelligence Service, or SIS, was officially acknowledged to even exist only in 1994. For most of the twentieth century, one of the most consequential intelligence organisations on earth operated without any public legal footing at all. Its chief signs documents with a single letter, C, written in green ink, a tradition stretching back to the very first director of the service. What began in 1909 as a small bureau tasked with watching the Imperial German Navy grew into a global human intelligence enterprise whose actions shaped coups, cold wars, and counterterrorism campaigns across more than a century. The questions this documentary will follow are the ones the historians and officers themselves wrestle with: how does a secret service balance effectiveness against accountability, and what does it cost when it gets that balance wrong?

• 2. The Green Ink Tradition

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  Captain Sir Mansfield George Smith-Cumming founded what would become SIS when the Secret Service Bureau opened on the 1st of October 1909. He typically dropped the Smith and signed all correspondence simply with his initial, C, in green ink. Every director of the service since has kept that same practice when signing documents, preserving a kind of anonymity through continuity.

  In the early years, Smith-Cumming treated the work with something close to sporting enthusiasm. He referred to espionage as a "capital sport" and expected agents to pick up their tradecraft on the job rather than in any formal classroom. One agent, Leslie Nicholson, later recalled his first posting in Prague: nobody gave him any tips on how to be a spy, how to approach sources, or how to extract useful information from unsuspecting experts. The training culture of the inter-war period was, by the agency's own later standards, casual almost to the point of negligence.

  Smith-Cumming died suddenly at his home on the 14th of June 1923, shortly before he had been due to retire. His successor, Admiral Sir Hugh Sinclair, took a more systematic approach, creating specialist sections for counter-espionage, economic intelligence, clandestine radio communications, and covert paramilitary action. Sinclair's Section D, which was designed for political covert action in wartime, would eventually become the foundation for the Special Operations Executive during the Second World War.

• 3. The Zinoviev Letter and Political Interference

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  In 1924, MI6 took an action that would shadow debates about intelligence and democracy for decades. A document had arrived at the MI6 resident at the British Embassy in Riga on the 9th of October 1924, purportedly from Grigory Zinoviev, the chief of the Communist International, instructing British communists to seize control of the Labour Party. The letter was a forgery, written in English, and yet MI6 leaked it to the Daily Mail, which published it on its front page on the 25th of October 1924.

  The effect was immediate and significant. The Zinoviev letter played a central role in the defeat of Ramsay MacDonald's minority Labour government and delivered the general election of the 29th of October 1924 to the Conservatives under Stanley Baldwin. Whether MI6 knew at the time that the letter was a forgery has never been fully established.

  The episode established an uncomfortable precedent. An intelligence agency had intervened, directly or indirectly, in a democratic election. The 1994 Intelligence Services Act, which finally placed SIS on a statutory footing, also created the parliamentary oversight structures, including the Intelligence and Security Committee and the Investigatory Powers Tribunal, which now provide public accountability for SIS operations.

• 4. Kim Philby and Soviet Penetration

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  In 1940, a journalist named Kim Philby, whose full name was Harold Adrian Russell Philby, applied for a vacancy in Section D of SIS. He was vetted by his friend Guy Burgess, who was himself a Soviet agent. Neither man's loyalties were known to the service at the time. Philby would go on to become one of the most damaging intelligence penetrations of any Western agency in the twentieth century.

  In early 1944, Philby took a position in MI6's re-established anti-Soviet section, Section IX. From there, he was able to pass to Soviet intelligence all British knowledge of Soviet operations, including material that the American Office of Strategic Services had shared with the British. In August 1945, when Soviet intelligence officer Konstantin Volkov attempted to defect to Britain and offered the names of Soviet agents working inside British intelligence, Philby received the memo and alerted his Soviet controllers. Volkov was arrested before he could defect.

  The damage extended into SIS operations in the field. George Blake, an officer who had been captured and interned during the Korean War, was turned as a Soviet agent during that internment. After returning and being treated as something of a hero, he was posted in 1953 to the Vienna station, where he compromised the tunnel operations there. He was then assigned to Operation Gold, the Berlin tunnel project, which the Soviets consequently knew about from its inception. Blake was eventually identified after a Polish defector, Michael Goleniewski, exposed him in 1961. He was tried, imprisoned, and then escaped in 1966, being exfiltrated to the USSR. The Cambridge Five, of which Philby was the most senior member, included four other SIS and MI5 officers: Anthony Blunt, Guy Burgess, John Cairncross, and Donald Maclean.

• 5. Oleg Penkovsky and the Cuban Missile Crisis

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  The Cold War was not a story only of Soviet penetration into British intelligence. In a joint operation with the American CIA, MI6 recruited a colonel inside the Soviet military intelligence organisation, the GRU, named Oleg Penkovsky. He ran as an agent for two years, delivering several thousand photographed documents during that time.

  Among the material Penkovsky provided were Red Army rocketry manuals. Those manuals turned out to be directly consequential. They allowed analysts at the US National Photographic Interpretation Center to recognise, in October 1962, the precise deployment pattern of Soviet SS-4 medium-range and SS-5 intermediate-range ballistic missiles when they appeared in aerial photographs of Cuba. The documentation Penkovsky had provided was the key to understanding what the photographs showed.

  Later in the Cold War, MI6 arguably reached a peak of operational success against the Soviet Union with the recruitment in the 1970s of Oleg Gordievsky, a KGB officer who SIS ran for nearly a decade. When his position became untenable, SIS successfully exfiltrated him from the Soviet Union across the Finnish border in 1985. The CIA assessed the intelligence provided by SIS's Polish sources in the same period as some of the most valuable intelligence ever collected. That assessment was backed by a $20 million payment to SIS to expand the Polish operation.

• 6. The Polish Contribution to World War Two

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  A two-volume study jointly produced by the United Kingdom and Poland in July 2005 revealed something that had been classified until that point: 48 percent of all intelligence reports received by British secret services from continental Europe during the years 1939-45 had originated from Polish sources.

  Polish intelligence had several structural advantages in providing this volume of material. Occupied Poland maintained long-standing traditions of insurgent organisation passed through generations, and those organisations had existing networks in emigrant Polish communities in Germany and France. Polish people were also used as forced labourers across the continent, placing them in proximity to military installations and key sites that they could observe and report on.

  The liaison between British and Polish intelligence was facilitated by SIS officer Wilfred Dunderdale. The reports that changed hands included advance warning of the Afrika Korps departing for Libya, intelligence on Vichy French intentions ahead of Operation Torch, and early warnings of both Operation Barbarossa and the German Caucasus campaign, Operation Edelweiss. Polish-sourced reporting on German secret weapons began in 1941. Through Operation Wildhorn, a British special operations flight airlifted a captured V-2 rocket from occupied Poland with the assistance of the Polish resistance. Polish secret agent Jan Karski also delivered the first Allied intelligence on the Holocaust to the British. A crucial foundation for all of this collaboration had been laid on the 26th and the 27th of July 1939, in Pyry near Warsaw, when British representatives including Dilly Knox and Alastair Denniston were introduced to Polish Enigma-decryption techniques, Zygalski sheets, and the cryptologic Bomba device.

• 7. Controversy and Accountability

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  During the Global War on Terror, SIS accepted intelligence from the CIA that had been obtained through torture, including through the extraordinary rendition programme. Craig Murray, the UK ambassador to Uzbekistan, wrote several memos critical of Britain's acceptance of such information and was subsequently dismissed from his post.

  On the 10th of January 2002, an MI6 officer conducted his first interview of a detainee held by the Americans in Afghanistan and reported back to London that aspects of how the detainee had been handled did not appear consistent with the Geneva Conventions. Two days later, instructions were sent to all MI5 and MI6 officers in Afghanistan stating that because detainees were not in British custody, the law did not require officers to intervene to prevent mistreatment.

  Prior to the 2003 invasion of Iraq, allegations emerged that SIS had run Operation Mass Appeal, a campaign to plant stories about Iraqi weapons of mass destruction in the media. The operation was exposed in a newspaper in December 2003. Former weapons inspector Scott Ritter claimed that SIS had recruited him in 1997 to help with a propaganda effort against Iraq, with the stated aim of convincing the public that Iraq posed a greater threat than it actually did. Lord Butler's subsequent review of weapons of mass destruction intelligence found that budget cuts in the mid-1990s had reduced SIS's Middle East operational capabilities by twenty-five percent and had weakened the Joint Intelligence Committee's ability to assess the quality of information it was receiving. These cuts were identified as major contributors to the UK's erroneous assessments before the invasion. Blaise Metreweli has served as the chief of SIS, the officer signing documents as C, since 2025.