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Security Service

The Security Service, also known as MI5, is responsible for protecting the UK against covertly organised threats to national security. These include terrorism, espionage and the proliferation of weapons of mass destruction. It also provides security advice to a range of other organisations.

Its role is defined by the Security Service Act 1989[External website], which put the Service onto a statutory footing for the first time. The Act formalised the Home Secretary's responsibility for the work of the Security Service, defines its functions and sets out the responsibilities of its Director General. In summary, the Service's functions are:

• to protect national security, and in particular protect against threats from espionage, terrorism and sabotage, from the agents of foreign powers, and from actions intended to overthrow or undermine parliamentary democracy by political, industrial or violent means;
• to safeguard the economic well-being of the UK against threats posed by the actions or intentions of persons outside the British Islands;
• to act in support of police and other law enforcement agencies in the prevention and detection of serious crime.

To fulfil these functions, the Security Service:

• investigates threats by gathering, analysing and assessing intelligence;
• counters the sources of threats;
• advises government and others on the nature of the threat, and on relevant protective security measures; and
• assists other agencies, organisations and government departments in combating threats.

Since the establishment of the Serious Organised Crime Agency, the Service has suspended work on serious crime in order to concentrate more resources on counter terrorism.

The Security Service Act also established oversight arrangements, which are described on the Accountability and Oversight page. The Home Secretary is answerable to Parliament for the work of the Security Service.

In collecting and assessing intelligence the Security Service is guided by the requirements and priorities established by the Joint Intelligence Committee and approved by Ministers.

The Security Service was established in 1909 as the domestic arm of the Secret Service Bureau, under Army Captain (later Major General Sir) Vernon Kell, tasked with countering German espionage. It became formally known as the Security Service (and theoretically stopped being called MI5) in 1931. At the same time it assumed wider responsibility for assessing threats to national security, which included communist and fascist subversion as well as espionage by hostile foreign powers. The Service's role changed significantly with the rise of terrorism and the end of the Cold War. Most of its resources now go into counter-terrorist work. Since 1992 it has been the lead agency for national security work in Great Britain, and will take on this role in Northern Ireland from 2007.

Although the Security Service works very closely with law enforcement organisations, its staff have no executive powers. Cases likely to result in prosecution are co-ordinated closely with the police, Crown Prosecution Service, or HM Immigration Service, or HM Revenue and Customs, who take any necessary action in accordance with their own responsibilities.

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