What is MI5?
To understand how Britain protects itself from threats at home, you must understand MI5. The Security Service operates as the UK’s domestic intelligence agency. From hunting Soviet spies during the Cold War to countering Russian assassinations and cyberattacks today, the agency guards the frontline of Britain’s internal security.
Origins and Mission
The British government created MI5 in 1909 to counter German espionage before the First World War. Over the century that followed, MI5 evolved from a small counterespionage unit into a professional service with broad powers to track hostile state activity and terrorism. Its core mandate remains the protection of national security inside the UK.
Structure and Oversight
MI5 reports to the Home Secretary and operates under the Intelligence Services Act of 1989. The Director General leads the service from its Thames House headquarters in London. Parliamentary committees provide oversight, but the agency maintains secrecy about its operations to preserve effectiveness against hostile actors.
Cold War Legacy
During the Cold War, MI5 fought a shadow battle with the KGB and GRU. It uncovered Soviet spy networks, neutralised moles inside Britain, and worked closely with MI6 and GCHQ to counter Russian influence. These experiences shaped its modern focus on counterintelligence and resilience against state-led operations.
Russia and Hybrid Threats
Today, MI5 views Russia as one of the UK’s most persistent threats. The 2006 poisoning of Alexander Litvinenko and the 2018 Salisbury nerve agent attack exposed the scale of Russian operations on British soil. The agency now tracks Russian cyber units, propaganda campaigns, and covert assets that aim to destabilise Britain and Europe.
Expanding Challenges
MI5 also combats terrorism, cybercrime, and espionage from other authoritarian states. Yet Russian hybrid warfare — combining disinformation, sabotage, and intelligence operations — remains central. The service must divide its resources across multiple threats while maintaining vigilance against Moscow’s covert actions.
Strategic Role
MI5 provides Britain with its shield at home. By countering Russian espionage, detecting hybrid threats, and cooperating with allies, it forms a critical part of Europe’s wider security network. Understanding MI5 means understanding how modern states defend themselves not just on foreign battlefields but within their own borders.
