Security Service

Overview

The Security Service is the United Kingdom's domestic security and counter-intelligence service. It is responsible for the protection of national security inside the United Kingdom against threats from espionage, terrorism, and the proliferation of weapons of mass destruction, and for the safeguarding of the economic well-being of the United Kingdom against threats posed by the actions or intentions of persons outside the British Islands. It is popularly known as MI5 — short for Military Intelligence, Section 5 — and operates under the authority of the Home Secretary.¹

The Service is headquartered at Thames House on Millbank, London, and is led by a Director General. Its existence was formally avowed by the Government in 1989, with the passage of the Security Service Act, which provided the first statutory basis for its activities. The Service does not have police powers and conducts its operations principally through investigation, surveillance, agent-running, and partnership with the police and Crown Prosecution Service.²

History & Origins

The Service was established in October 1909 as the Home Section of the Secret Service Bureau, under the same Committee of Imperial Defence sub-committee that produced the Secret Intelligence Service. Its first head, Captain Vernon Kell — known as "K" — served from 1909 until his dismissal in 1940, the longest tenure of any head of a British intelligence agency.³

The Service's first major sustained operational period was directed against German espionage in the lead-up to and during the First World War. The interwar period saw expansion against Soviet operations and the surveillance of British communist and fascist political organisations. The Second World War produced the Service's most operationally consequential successes, including the Double-Cross System under the supervision of the XX Committee — a coordinated programme through which all known German agents in the United Kingdom were turned and used to feed deceptive information back to the German military intelligence service.⁴

The post-war period brought the Service's most consequential failures. The 1951 defection of Donald Maclean and Guy Burgess, the 1963 confirmation of Kim Philby as a long-term Soviet penetration, and the 1979 unmasking of Anthony Blunt as a former Service-period KGB asset — Blunt had served in the Service during the war — together formed the institutional record that the Service was for decades unable to publicly address.⁵

The Service's modern statutory form was established by the Security Service Act 1989 and significantly extended by the Security Service Act 1996, the Regulation of Investigatory Powers Act 2000, the Justice and Security Act 2013, and the Investigatory Powers Act 2016.²

Mandate & Jurisdiction

The Service's authorities are specified in the Security Service Act 1989, as amended. Its statutory functions are:

• the protection of national security and, in particular, its protection against threats from espionage, terrorism, and sabotage, from the activities of agents of foreign powers, and from actions intended to overthrow or undermine parliamentary democracy by political, industrial, or violent means;
• the safeguarding of the economic well-being of the United Kingdom against threats posed by the actions or intentions of persons outside the British Islands;
• to act in support of the activities of police forces, the National Crime Agency, and other law-enforcement agencies in the prevention and detection of serious crime.⁶

The Service operates inside the United Kingdom; foreign intelligence is the responsibility of the Secret Intelligence Service. Since 2007 the Service has been the lead UK agency for counter-terrorism, displacing what had been a Special Branch–led role.

Notable Operations

Confirmed Double-Cross System (1939–1945). The wartime programme through which all known German agents in the United Kingdom were captured, turned, and run as double agents to feed deceptive information back to the Abwehr. The system fed material supporting the Operation Bodyguard and Operation Fortitude deception plans for the Normandy landings. The official history was published in 1972.⁴

Confirmed Identification of Kim Philby (1949–1963). The Service's prolonged investigation of penetration in the Foreign Office and intelligence services, leading to the eventual identification of Donald Maclean (1951), Guy Burgess (1951), Kim Philby (officially 1963), Anthony Blunt (formally 1964; publicly 1979), and John Cairncross. Subsequent declassified records and the official histories established the institutional cost of the long delay in pursuing the identifications.⁵

Confirmed Counter-IRA operations (1969–1998). The Service's sustained operational effort against the Provisional IRA and other paramilitary organisations during the Troubles. The 2003 Stevens Inquiry and the 2012 de Silva Review documented elements of agent-running and collusion that have remained the subject of public-record controversy.⁷

Confirmed Counter-terrorism after 2001. The Service's post-2001 expansion as the UK lead for counter-terrorism investigation included disruption of the 2006 transatlantic aircraft plot — leading to the convictions of Abdulla Ahmed Ali and others — and the investigation of the 7 July 2005 London transport bombings. The Intelligence and Security Committee's 2006 report on the 7 July attacks identified specific issues of coverage and assessment.⁸

Controversies & Abuses

Confirmed Surveillance of MPs, journalists, and civil-society organisations. Successive declassified records and the work of the Investigatory Powers Tribunal have documented Service surveillance, in earlier decades, of Members of Parliament, journalists, the National Council for Civil Liberties (now Liberty), and trade-union officials in circumstances that successor reviews concluded had been improper. The Wilson Doctrine — the convention against tapping MPs' communications — was repeatedly tested by such cases.⁹

Confirmed Loyalist agent-running in Northern Ireland. The Stevens Inquiry (2003), the de Silva Review (2012), and the Police Ombudsman for Northern Ireland's 2007 Operation Ballast report identified cases of Service and other-agency agent-running with loyalist paramilitary organisations in which agents had been involved in serious criminality, including murder, while reporting to handlers. The full record remains substantially classified.⁷

Confirmed 2017 Manchester Arena bombing review. The Intelligence and Security Committee's 2018 report and the Saunders Inquiry's 2022 report on the Manchester Arena attack identified specific failures in Service handling of intelligence on the bomber, Salman Abedi. The Service's Director General publicly accepted the findings.¹⁰

Confirmed Historical files on persons of interest. The release in 2003, 2014, 2018, and successive years of declassified Service personal files at the National Archives has confirmed long-running surveillance of figures including the writer Doris Lessing, the actor Vanessa Redgrave, the architect Berthold Lubetkin, and successive Labour MPs.¹¹

Notable Figures

• Captain Sir Vernon Kell — First Director, 1909–1940. Founder of the Service; dismissed in 1940 by Winston Churchill.
• Sir Roger Hollis — Director General, 1956–1965. Subject of subsequent unsubstantiated allegations of Soviet penetration; the 1981 Trend inquiry concluded the allegations were not proved.
• Stella Rimington — Director General, 1992–1996. First woman to hold the post and the first Director General to be publicly named in office.¹²
• Eliza Manningham-Buller — Director General, 2002–2007. Period of post-2001 counter-terrorism expansion.
• Jonathan Evans (Lord Evans of Weardale) — Director General, 2007–2013. Period of the Olympics security operation.
• Andrew Parker — Director General, 2013–2020.
• Sir Ken McCallum — Director General, 2020–present.

Oversight & Accountability

The Service is subject to oversight by the Home Secretary as the responsible minister; the Intelligence and Security Committee of Parliament, established in its current statutory form by the Justice and Security Act 2013; the Investigatory Powers Commissioner and the Investigatory Powers Tribunal; and the Independent Reviewer of Terrorism Legislation.

The Investigatory Powers Act 2016 placed the Service's targeted-equipment-interference, bulk-personal-dataset, and bulk-communications-data powers on a more detailed statutory footing, with judicial commissioner approval required for the most intrusive warrants. Investigatory Powers Tribunal cases — most prominently the 2018 ruling on the use of agents engaged in serious criminality — have provided the most regular public-record judicial scrutiny of Service activities.¹³

Sources & Further Reading

1. Security Service Act 1989, c. 5; MI5, "About MI5," mi5.gov.uk.
2. Christopher Andrew, The Defence of the Realm: The Authorized History of MI5 (Allen Lane, 2009).
3. Andrew, Defence of the Realm, chapters 1–3; Christopher Andrew, Secret Service: The Making of the British Intelligence Community (Heinemann, 1985).
4. J. C. Masterman, The Double-Cross System in the War of 1939 to 1945 (Yale University Press, 1972); Andrew, Defence of the Realm, chapters 7–9.
5. Andrew, Defence of the Realm, sections on Soviet penetration; Ben Macintyre, A Spy Among Friends (Crown, 2014).
6. Security Service Act 1989, section 1, as amended.
7. Sir John Stevens, Stevens Inquiry: Overview and Recommendations, 17 April 2003; Sir Desmond de Silva, The Report of the Patrick Finucane Review, HC 802, 2012; Police Ombudsman for Northern Ireland, Operation Ballast: Statement by the Police Ombudsman, 22 January 2007.
8. Intelligence and Security Committee of Parliament, Report into the London Terrorist Attacks on 7 July 2005, Cm 6785, May 2006; Could 7/7 Have Been Prevented?: Review of the Intelligence on the London Terrorist Attacks, Cm 7617, May 2009.
9. Investigatory Powers Tribunal judgments and opinions, public-database editions; Andrew, Defence of the Realm, sections on domestic political surveillance.
10. Intelligence and Security Committee of Parliament, The 2017 Attacks: What needs to change?, HC 1694, 22 November 2018; Sir John Saunders, Manchester Arena Inquiry: Volume 3 — Radicalisation and Preventability, 2 March 2023.
11. National Archives, KV 2 series releases, multiple tranches 2003–2024.
12. Stella Rimington, Open Secret: The Autobiography of the Former Director-General of MI5 (Hutchinson, 2001).
13. Investigatory Powers Tribunal, Privacy International & Others v. Secretary of State for Foreign and Commonwealth Affairs & Others, IPT/17/86/CH, 20 December 2019.