MI5's headquarters in London
23 January 2022 08:00 AM


23 January 2022

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 was on counter-espionage directed against foreign subversion: today, it is focused on counter-terrorism work, fighting organised and cyber crime.

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

MI5 currently employs about 4,400 people, 43% of which are women, half of whom are under 40 years old, 9% of whom are from black or ethnic minority backgrounds and 4% of whom have a disability.

Some 67% of MI5’s resources are focussed on counter-terrorism, 20% on Northern Ireland related terrorism, and 13% on counter-espionage, counter-proliferation and protective security.

Who runs MI5?

  • MI5 is a government department under the authority of the Home Secretary. The UK’s two other intelligence agencies (SIS (MI6) and GCHQ) operate under the authority of the Foreign Secretary.
  • MI5 is currently headed by its Director General, Ken McCallum. Mr McCallum grew up in Glasgow, and holds a degree in Mathematics from Glasgow University.

A long time employee of MI5, he was a former Deputy Director General of the Service, and led MI5’s response to the attempted assassination of Sergei Skripal in Salisbury in 2018.

  • The Director General of MI5 is responsible for the operations and efficiency of the agency, for making sure that MI5 is politically impartial, and for obtaining information only in accordance with MI5’s statutory responsibilities and to prevent or detect serious crime.

MI5’s headquarters in London

Under the Justice and Security Act 2013 and the accompanying Memorandum of Understanding, Parliament’s Intelligence and Security Committee oversees the policies, expenditure, administration and operations of MI5, MI6, and GCHQ. The Committee consists of nine Members, drawn from both Houses off Parliament.

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