Early years The Security Service is derived from the
Secret Service Bureau, founded in 1909, and concentrating originally on the activities of the
Imperial German government, as a joint initiative of the
Admiralty and the
War Office. The Bureau was initially split into naval and army sections which, over time, specialised respectively in foreign target
espionage and internal
counter-espionage activities. The former specialisation was a result of a growing interest at the Admiralty, at the time, in intelligence regarding the fleet of the
Imperial German Navy. This division was formalised, as separate home and foreign sections, prior to the beginning of the
First World War. Following a number of administrative changes, the home section became known as
Directorate of Military Intelligence, Section 5 and the abbreviation MI5, the name by which it is still known in popular culture. (The foreign/naval section of the Secret Service Bureau was to become the basis of the later Secret Intelligence Service, or
MI6). The founding head of the Army section was
Vernon Kell of the
South Staffordshire Regiment, who remained in that role until the early part of the
Second World War. Its role was originally quite restricted, as the section existed solely to ensure national security through counter-espionage. With a small staff, and working in conjunction with the
Special Branch of the
Metropolitan Police, the service was responsible for overall direction and the identification of foreign agents, while Special Branch provided the manpower for the investigation of their affairs, arrest and interrogation.
First World War On the day after the declaration of the First World War, the Home Secretary,
Reginald McKenna, announced that "within the last twenty-four hours no fewer than twenty-one spies, or suspected spies, have been arrested in various places all over the country, chiefly in important military or naval centres, some of them long known to the authorities to be spies". These arrests have provoked recent historical controversy. According to the official history of MI5, the actual number of agents identified was 22, and Kell had started sending out letters to local police forces on 29 July, giving them advance warning of arrests to be made as soon as war was declared. Portsmouth Constabulary jumped the gun and arrested one on 3 August, and not all of the 22 were in custody by the time that McKenna made his speech, but the official history regards the incident as a devastating blow to
Imperial Germany, which deprived them of their entire spy ring, and specifically upset the Kaiser. However, in 2006, historian Nicholas Hiley published an article entitled "Entering the Lists" in the journal
Intelligence and National Security, outlining the products of his research into recently opened files on spies arrested at the start of the First World War. Hiley was sent an advance copy of the official history, and objected to the retelling of the story. He later wrote another article, "Re-entering the Lists", which asserted that the list of those arrested published in the official history was concocted from later case histories. In the meantime, MI5's role had grown substantially. Due to the spy hysteria, MI5 had formed with far more resources than it actually needed to track down German spies. As is common within governmental bureaucracies, this caused the service to expand its role to use its spare resources. MI5 acquired many additional responsibilities during the war. Most significantly, its strict counter-espionage role blurred considerably. It acquired a much more political role, involving the surveillance not merely of foreign agents, but also of
pacifist and anti-
conscription organisations, and of
organised labour. This was justified by citing the common belief that foreign influence was at the root of these organisations. Thus, by the end of the First World War, MI5 was a fully-fledged investigating force (although it never had powers of arrest), in addition to being a counter-espionage agency. The expansion of this role continued after a brief post-war power struggle with the head of the
Special Branch, Sir
Basil Thomson.
Inter-war period MI5 proved consistently successful throughout the rest of the 1910s and 1920s in its core counter-espionage role. In post-war years, attention turned to attempts by the
Soviet Union and the
Comintern to surreptitiously support revolutionary activities within Britain. MI5's expertise, combined with the early incompetence of the Soviets, meant the bureau was successful in correctly identifying and closely monitoring these activities. After the First World War, budget-conscious politicians regarded Kell's department as unnecessary. In 1919, MI5's budget was slashed from £100,000 to just £35,000, and its establishment from over 800 officers to a mere 12. At the same time, Sir
Basil Thomson of
Special Branch was appointed
Director of Home Intelligence, in supreme command of all domestic counter-insurgency and counter-intelligence investigations. Consequently, as official MI5 historian
Christopher Andrew has noted in his official history
Defence of the Realm (2010), MI5 had no clearly defined role in the
Irish War of Independence of 1919–1921. To further worsen the situation, several of Kell's officers defected to Thomson's new agency, the Home Intelligence Directorate. MI5 therefore undertook no tangible intelligence operations of consequence during the conflict. MI5 did undertake the training of
British Army case-officers from the Department of Military Intelligence (DMI), for the Army's so-called "Silent Section", otherwise known as M04(x). In 1921, Sir
Warren Fisher, the government inspector-general for civil-service affairs, conducted a thorough review of the operations and expenditures of Basil Thomson's Home Intelligence Directorate. He issued a scathing report, accusing Thomson of wasting both money and resources, and conducting redundant as well as ineffectual operations. Shortly thereafter, in a private meeting with Prime Minister
David Lloyd George, Sir Basil Thomson was sacked, and the Home Intelligence Directorate was formally abolished. With Thomson out of the way,
Special Branch was returned to the command of the Commissioner of The Criminal Investigation Division at
Scotland Yard. Only then was Vernon Kell able once again to rebuild MI5 and restore it to its former place as Britain's chief domestic intelligence agency. MI5 operated in Italy during the inter-war period, and helped
Benito Mussolini get his start in politics with a £100 weekly wage. The NKVD, meanwhile, had evolved more sophisticated methods; it began to recruit agents from within the elite universities (most notably from
Cambridge University) which traditionally formed the recruitment pool for the
Civil Service. Many of these recruits succeeded in gaining positions within the government, and even within the intelligence services themselves. The most famous of these spies were
Kim Philby,
Donald Maclean,
Guy Burgess,
Anthony Blunt, and
John Cairncross. Undetected until after the
Second World War, they became known as the
Cambridge Five. All save Maclean served with MI5 or MI6 during the war, and the spy ring would pass more than 16,000 documents to the Soviets.
Second World War One of the earliest actions of
Winston Churchill on coming to power in early 1940 was to sack the agency's long-term head,
Vernon Kell. He was replaced initially by the ineffective
Oswald Allen Harker, as Acting Director General. Harker in turn was quickly replaced by
David Petrie, a
Secret Intelligence Service (SIS) man, with Harker remaining as his deputy. With the ending of the
Battle of Britain, and the abandonment of invasion plans (correctly reported by both SIS and the
Bletchley Park Ultra project), the spy scare eased, and the internment policy was gradually reversed. This eased pressure on MI5, and allowed it to concentrate on its major wartime success, the so-called
'double-cross' system. This was a system based on an internal memo drafted by an MI5 officer in 1936, which criticised the long-standing policy of arresting and sending to trial all enemy agents discovered by MI5. Several had offered to defect to Britain when captured; before 1939, such requests were invariably turned down. The memo advocated attempting to 'turn' captured agents wherever possible, and use them to mislead enemy intelligence agencies. This suggestion was turned into a massive and well-tuned system of deception during the Second World War. All foreigners entering the country were processed at the
London Reception Centre (LRC) at the
Royal Victoria Patriotic Building, which was operated by MI5 subsection B1D; 30,000 were inspected at LRC. Captured enemy agents were taken to
Camp 020,
Latchmere House, for interrogation. This was commanded by Colonel Robin Stephens. There was a reserve camp, Camp 020R, at
Huntercombe, which was used mainly for long term detention of prisoners. It is believed that two MI5 officers participated in "a gentle interrogation" given to the senior Nazi
Heinrich Himmler after his arrest at a military checkpoint in the northern German village of Bremervörde in May 1945. Himmler subsequently killed himself during a medical examination by a British officer by means of a cyanide capsule that he had concealed in his mouth. One of the MI5 officers,
Sidney Henry Noakes of the
Intelligence Corps, was subsequently given permission to keep Himmler's
braces and the forged identity document that had led to his arrest.
Post-Second World War The Prime Minister's personal responsibility for the service was delegated to the
Home Secretary David Maxwell-Fyfe in 1952, with a directive issued by the Home Secretary setting out the role and objectives of the Director General. The service was subsequently placed on a statutory basis in 1989 with the introduction of the Security Service Act. This was the first government acknowledgement of the existence of the service. The post-war period was a difficult time for the service, with a significant change in the threat as the
Cold War began, being challenged by an extremely active
KGB, and increasing incidence of the Northern Ireland conflict, and international
terrorism. Whilst little has yet been released regarding the successes of the service, there have been a number of intelligence failures which have created embarrassment for both the service and the government. For instance, in 1983, one of its officers,
Michael Bettaney, was caught trying to sell information to the KGB. He was subsequently convicted of espionage. Following the Bettaney case,
Philip Woodfield was appointed as a staff counsellor for the security and intelligence services. His role was to be available to be consulted by any member or former member of the security and intelligence services who had "anxieties relating to the work of his or her service" that it had not been possible to allay through the ordinary processes of management-staff relations, including proposals for publications. The service was instrumental in breaking up a large
Soviet spy ring at the start of the 1970s, with 105 Soviet embassy staff known or suspected to be involved in intelligence activities being expelled from the country in 1971. Controversy arose when it was alleged that the service was monitoring
trade unions and left-wing politicians. A file was kept on Labour Prime Minister
Harold Wilson from 1945, when he became a
Member of Parliament (MP), although the agency's official historian,
Christopher Andrew maintains that his fears of MI5 conspiracies and bugging were unfounded. As Home Secretary, the
Labour MP
Jack Straw discovered the existence of his own file dating from his days as a
student radical. One of the most significant and far-reaching failures was an inability to conclusively detect and apprehend the '
Cambridge Five' spy ring, which had formed in the inter-war years, and achieved great success in penetrating the government, and the intelligence agencies themselves. Another spy ring, the
Portland spy ring, exposed after a tip-off by Soviet defector
Michael Goleniewski, led to an extensive MI5 surveillance operation. In 1991, MI5 revealed its head publicly for the first time and declassified some information, "such as the number of its employees and its organizational structure." Following the
United States invasion of Afghanistan, on 9 January 2002, the first MI5 staff arrived at
Bagram. On 12 January 2002, following a report by an
MI6 officer that a detainee appeared to have been mistreated before, an MI6 officer was sent instructions that were copied to all MI5 and MI6 staff in Afghanistan about how to deal with concerns over mistreatment, referring to signs of abuse: 'Given that they are not within our custody or control, the law does not require you to intervene to protect this'. It went on to say that the Americans had to understand that the UK did not condone such mistreatment, and that a complaint should be made to a senior US official if there was any coercion by the US in conjunction with an MI6 interview.
Counter-terrorism The end of the
Cold War resulted in a change in emphasis for the operations of the service, assuming responsibility for the investigation of all
Irish republican activity within Britain, and increasing the effort countering other forms of terrorism, particularly in more recent years the more widespread threat of
Islamic extremism. Whilst British security forces have provided support in countering the activities of both
Irish republican and
Ulster loyalist paramilitary groups in
Northern Ireland since the early 1970s, republicans have often accused these forces of
collusion with loyalists. In 2006, an Irish government committee inquiry claimed to have found nine instances of collusion between British security forces and loyalist paramilitaries during the 1970s. In 2012, a document-based review by the British barrister
Sir Desmond de Silva into the 1989 murder of Belfast solicitor
Pat Finucane found that MI5 had spread propaganda against Finucane in the years prior to his death and took no steps to protect him from loyalist paramilitaries. The review disclosed that MI5 assessments of
Ulster Defence Association intelligence consistently noted that the majority came from MI5 sources, with an assessment in 1985 finding 85% of the intelligence originating from MI5. On 10 October 2007, the lead responsibility for national security intelligence in Northern Ireland returned to the Security Service from the
Police Service of Northern Ireland (PSNI), that had been devolved in 1976 to the
Royal Ulster Constabulary (RUC) during
Ulsterisation. During April 2010, the
Real IRA detonated a 120 lb
car bomb outside Palace Barracks in
County Down, which is the headquarters of MI5 in Northern Ireland and also home to the 2nd Battalion
The Mercian Regiment. MI5 is understood to have a close working relationship with the
Republic of Ireland's
Special Detective Unit (SDU), the counter-terrorism and counter-intelligence section of the
Garda Síochána (national police), particularly with regards to threats from
dissident republican terrorism and
Islamic terrorism. Executive liaison groups enable MI5 to safely share secret, sensitive, and often raw intelligence with the police, on which decisions can be made about how best to gather evidence and prosecute suspects in the courts. Each organisation works in partnership throughout the investigation, but MI5 retain the lead for collecting, assessing and exploiting intelligence. The police take lead responsibility for gathering evidence, obtaining arrests, and preventing risks to the public.
Serious crime In 1996, legislation formalised the extension of the Security Service's statutory remit to include supporting the law enforcement agencies in their work against serious crime. Tasking was reactive, acting at the request of law enforcement bodies such as the
National Criminal Intelligence Service (NCIS), for whom MI5 officers performed electronic surveillance and eavesdropping duties during
Operation Trinity.
Surveillance In 2001, after the
September 11 attacks in the US, MI5 started collecting bulk telephone communications data under a little understood general power of the
Telecommunications Act 1984 (instead of the
Regulation of Investigatory Powers Act 2000 which would have brought independent oversight and regulation). This was kept secret until announced by the
Home Secretary in 2015. This power was replaced by the
Investigatory Powers Act 2016 which introduced new surveillance powers overseen by the Investigatory Powers Commission (IPC) it introduces. In July 2006, parliamentarian
Norman Baker accused the British Government of "hoarding information about people who pose no danger to this country", after it emerged that MI5 holds secret files on 272,000 individuals, equivalent to one in 160 adults. It had previously been revealed that a '
traffic light' system operates: • Green: active; about 10% of files • Amber: enquiries prohibited, further information may be added; about 46% of files • Red: enquiries prohibited, substantial information may not be added; about 44% of files.
Participation of MI5 officers in criminal activity In March 2018, the government acknowledged that MI5 officers are allowed to authorise agents to commit criminal activity in the UK. Maya Foa, the director of
Reprieve, said: "After a seven-month legal battle, the prime minister has finally been forced to publish her secret order, but we are a long way from having transparency. The public and parliament are still being denied the guidance that says when British spies can commit criminal offences, and how far they can go. Authorised criminality is the most intrusive power a state can wield. Theresa May must publish this guidance without delay". In November 2019, four
human rights organisations claimed that the UK government has a policy dating from the 1990s to allow MI5 officers to authorise agents or informers to participate in crime, and to immunise them against prosecution for criminal actions. The organisations said the policy allowed MI5 officers to authorise agents and informers to participate in criminal activities that protected national security or the economic well-being of the UK. The organisations took the UK government to the
Investigatory Powers Tribunal, seeking to have it declare the policy illegal, and to issue an injunction against further 'unlawful conduct'. In December 2019, the tribunal dismissed the request of the human rights organisations in a 3-to-2 decision. The potential criminal activities include murder, kidnap, and torture, according to a
Bloomberg report.
Allegations of collusion in torture In October 2020,
Rangzieb Ahmed brought a civil claim against MI5, alleging that Pakistan's
Inter-Services Intelligence agency had arrested him in 2006, and that MI5 had colluded in torture by submitting questions which were put to him under torture in Pakistan. This claim was rejected by the High Court on 16 December 2020.
Domestic abuse scandal In May 2022, the BBC reported on an unnamed MI5 agent, 'X', domestically abusing his partner, despite the British government's attempts to block this. BBC journalists subsequently discovered that MI5 lied to courts, suggesting that the organisation was unaware of X's behaviour, including his far-right extremist views. An ongoing High Court case began in June 2025, with MI5 accepting that X's status should no longer be protected, after previously
neither confirming nor denying his role as an agent. ==Buildings==