What is MI5?

MI5, properly known as the Security Service, is the UK's security intelligence agency. Although the "MI" stands for "Military Intelligence", MI5 is a civilian agency without formal executive powers.

MI5 is principally concerned with countering threats to domestic security – in contrast to MI6, which is concerned with external security. Historically, MI5's focus has been counter-espionage directed against foreign subversion: today, it is focused on counter-terrorism work and fighting organised and serious crime.

MI5 today works primarily in liaison with other agencies, particularly the Special Branch of police forces. Its officers do not have any powers of arrest or detention.


MI5 has its origins in the Secret Service Bureau, founded in 1909 to control the UK's intelligence activities. Originally split into naval and army sections, these branches rapidly came to focus on overseas and domestic security respectively. This division was formalised with the separation of the Secret Intelligence Service (MI6) in 1911. The "MI" designations were introduced in 1916, with the organisations' transfer to the Directorate of Military Intelligence.

Highly successful in rooting out German spies in the run-up to the First World War, MI5 soon widened the scope of its attention to the pacifist and labour movements – in the belief that these groups were being manipulated by foreign provocateurs. It was also active in Ireland, although it was largely unsuccessful in infiltrating the IRA.

After the Russian Revolution of 1917, the threat posed by communism became a central focus for MI5 – leading it on occasion into sensitive political areas. The most notorious episode of this period was the "Zinoviev Letter" affair of 1924 – a letter from the head of the Comintern urging British socialists to revolt was leaked to the press, resulting in Labour losing the general election. The letter was later found to have been the work of anti-socialist elements within MI5 and MI6.

Nonetheless, MI5 was unsuccessful in preventing significant Soviet infilitration during the 1930s: the most famous case being that of the "Cambridge Five" – one of whom, Kim Philby, was a British intelligence officer himself – whose espionage for the USSR went undetected until the 1960s.

In the postwar era, MI5's attention was firmly fixed on the USSR and its allies. The revival of Irish terrorism in the late 1960s drew it heavily into counter-terrorism work, as well as counter-espionage. However, allegations of political subversion continued to dog the Service: the Labour prime minister Harold Wilson was convinced that MI5 was plotting against him, a claim repeated by the former MI5 officer Peter Wright in his 1987 memoir, "Spycatcher".

Until 1989, successive governments continued to deny the existence of MI5 and its fellow intelligence agencies. The "Spycatcher" affair was therefore a considerable blow for the Service: despite the Thatcher government's attempts to prevent publication, the book obtained worldwide attention, outlining allegations of incompetence in MI5, a plot to assassinate the Egyptian president Kamal Nasser, and resurrecting the claim that the head of MI5 during the 1960s, Sir Roger Hollis, was a Soviet agent (officially denied by the Trend inquiry of 1974).

In the wake of "Spycatcher", the Security Services Act 1989 formally acknowledged the existence of MI5, and the Intelligence Services Act 1994 established the Parliamentary Intelligence and Security Committee to reinforce Parliamentary accountability. Under the leadership of the recognisable figure of director-general Stella Rimington, MI5 began to move out of the shadows. Surveillance work was subjected to the scrutiny of the Interception Commissioner under the Regulation of Investigatory Powers Act 2000.

With the collapse of the Soviet Union in 1989 and the decline of Irish terrorism in the mid-1990s (due in part, many argue, to the successes of MI5), the agency's principal foci had been considerably diminished. As a result, in 1996, MI5 expanded its remit into intelligence work relating to conventional criminal activity – a substantial change in its role, and one which many condemned as turning the organisation into a de facto "secret police force".

MI5 was shaken again in 1997, when another former officer, David Shayler published allegations of incompetence and an MI6 plot to assassinate Libyan leader Colonel Gadaffi. Once again, the Government's attempts to silence Shayler – efforts which culminated in demands that he be extradited from France – raised the profile of his claims considerably. In November 2002, Shayler was sentenced to six months imprisonment for breaching the Official Secrets Act.

Since the events of September 11 2001, and the emergence of international terrorism as a major concern for Western governments, MI5 has found a new focus of attention. Its experience in combating the IRA has been useful in addressing the new terrorist threat.


Every state in history has maintained its secret intelligence services, but their existence is always problematic for open democratic states, particularly in the age of mass media. The openness required in democratic societies is necessarily at odds with the secrecy of intelligence agencies. As such, revelations about their work has often been a cause of public scandal.

Today, MI5 has a public commitment to "legality; integrity; objectivity; a sense of proportion about our work; and respect and consideration for each other and for those with whom we work outside the Service". While allegations about its activities in much of the recent past remain necessarily contentious, there is a widespread belief that MI5 has frequently operated outside the law. Where such instances have come into the open, the culprits have usually been dismissed as "rogue" elements.

The agency has long had an ambiguous relationship with the Labour Party and the left in general. One of David Shayler's revelations was that MI5 had maintained files on leading Labour politicians, including Jack Straw and Peter Mandelson. Part of the perceived hostility is widely believed to stem from MI5's position at the heart of the "Establishment". Prominent politicians and journalists claim to have been approached by MI5 asking them to provide information on colleagues. Despite extensive efforts to open itself up and diversify its membership in recent years, large sections of the public continue to regard the intelligence services as Oxbridge-dominated, upper and upper-middle class, white and politically conservative.

MI5's move into the field of conventional crime under the Security Services Act 1996 was a highly contentious development. Unlike the police and other criminal investigation bodies, MI5 had little experience of working in the open, and had previously had little focus on obtaining convictions. This lack of organisational fit concerned many that the agency was being engaged as a "secret police force".

MI5 maintains that it only becomes involved in criminal investigations when tasked to do so by another law enforcement agency, which hopes to benefit from its intelligence expertise. The Service states that most of the work it has done in this regard has been in relation to drug trafficking.

It is necessarily difficult to know precisely what a secret intelligence agency does. MI5 and the Government insist that the Security Service acts only in line with the remit outlined in the Security Services Act, and that the reforms of the last ten years have rendered it fully politically and judicially accountable. Many, however, are unwilling to believe this.

Most recently MI5 has had to refute allegations that it was complicit in acts of torture carried out in the aftermath of 9/11 on terrorist suspects detained abroad. In July 2010 the Prime Minister, David Cameron, announced that a non-statutory inquiry would be established to examine whether, and if so to what extent, the UK's government and intelligence agencies were involved in improper treatment of detainees held by other countries.

Mr Cameron stressed that the allegations had not been proven and he praised the "tremendous acts of bravery" carried out by intelligence officers who "track terrorist threats and disrupt plots..without any public-or, often, even private-recognition, and despite the massive personal risks to their safety." Nevertheless he said there were "questions over the degree to which British officers were working with foreign security services who were treating detainees in ways they should not have done" and that these "issues of the past" had to be resolved.

In particular claims by a former Guantanamo detainee and Ethiopian born UK resident Binyam Mohamed that an MI5 officer had been complicit in his torture in 2002 resulted in an inquiry being launched by Scotland Yard. However, in November 2010 the director of public prosecutions, Keir Starmer, announced that there was "insufficient evidence" to prosecute the officer.

In June 2012, MI5 director-general Jonathan Evans reported that the  Royal United Services Institute had identified 43 potential plots or serious incidents in the UK since 9/11.

Speaking at the Lord Mayor's Annual Defence and Security Lecture, Mr Evans said the Security Service assessment was that Britain had experienced "a credible terrorist attack plot" about once a year since 9/11, up until the present time, with a plot by Al Qaida in Yemen to blow up an airliner over the Atlantic narrowly averted in May 2012.

However, he believed that recent investment in counter-terrorism "has worked", with the joint intelligence agencies and the police identifying, disrupting and suppressing terrorism before it succeeds. "You could say that we are near to reaching a form of stalemate – they haven’t stopped trying but we have got better at stopping them. That is normally as much as security on its own can achieve," he said.  He stressed the need to tackle the underlying issues and circumstances "through political effort."

Mr Evans also warned that parts of the Arab world had once more become "a permissive environment for Al Qaida." He described this as "a new and worrying development" which he predicted could get worse as events unfold. "We will have to manage the short term risks if there is to be a longer-term reward from the Arab Spring," he said.


The Security Service has been listed as one of the top 100 employers in the UK for lesbian, gay and bisexual people. MI5 has also been named the fastest rising employer, moving from 134 to 62 in the  Stonewall Workplace Equality Index 2012.

Source: MI5 – January 2012

New records released today by the Security Service (MI5) include files on the silent-era film star Charlie Chaplin, the Dutch double-agent Folkert Van Koutrik and details of a Nazi plan to produce fake British banknotes.
This release contains 86 files and brings the total number of Security Service records held at The National Archives to 4,926.

Source: National Archives – February 2012


"In back rooms and in cars and on the streets of this country there is no shortage of individuals talking about wanting to mount terrorist attacks here. We see them regularly in our intelligence investigations.
"And others in various parts of the world have the same ambitions."

MI5 director-general Jonathan Evans – June 2012