MI5

MI5, officially the Security Service, is the United Kingdom's domestic counter-intelligence and security agency. Its primary mission is to protect national security by identifying and countering threats within the UK, including terrorism, espionage, cyber attacks, and attempts to procure weapons of mass destruction. It operates in conjunction with the police and other parts of the UK intelligence community to detect and disrupt hostile activity on British soil.

The agency traces its origins to 1909, when it began as the Secret Service Bureau to counter foreign espionage. It was renamed the Security Service in 1931 and is commonly known as MI5. The Security Service Act 1989 formalised its statutory basis and objectives, situating it within the framework of the UK’s intelligence community.

Functions and methods include collecting and analysing intelligence related to internal threats, conducting protective security work, and providing actionable intelligence to assist police and other authorities. MI5 coordinates with international partners for counterterrorism and counterespionage and plays a role in safeguarding critical infrastructure and sensitive information. Its operations are conducted under legal safeguards and oversight designed to balance security needs with civil liberties.

Oversight and governance involve parliamentary and statutory controls. The service reports to the Home Secretary and is subject to oversight by Parliament’s Intelligence and Security Committee, as well as mechanisms established by the Intelligence Services Act 1994 and the Investigatory Powers Act 2016.

Public profile and transparency are limited due to the sensitive nature of its work. MI5 collaborates with other UK agencies, notably MI6 and GCHQ, and maintains international cooperation with allied partners, including Five Eyes, to address cross-border security threats.