MI5 protects the UK against threats to national security

The role of MI5, as defined in the Security Service Act 1989, is "the protection of national security and in particular its protection against threats such as terrorism, espionage and sabotage, the activities of agents of foreign powers, and from actions intended to overthrow or undermine parliamentary democracy by political, industrial or violent means".

Our work is guided by the government's overall strategy to counter threats to the UK's national security. For more information on this strategy, see:

The national security strategy – a strong Britain in an age of uncertainty

The strategic defence and security review: securing Britain in an age of uncertainty

Threats to national security

The main threats to national security that MI5 counters are terrorism, espionage, cyber threats and the proliferation of weapons of mass destruction.

Protective security

Since its earliest days, MI5 has worked to reduce the UK’s national security vulnerabilities. The National Protective Security Authority (NPSA) is part of MI5 and offers advice to businesses and organisations of all shapes and sizes to help keep them and their customers safe from a range of national security threats. This include providing advice to the UK’s critical national infrastructure – the key assets that are vital to the continued delivery and integrity of essential public services.

NPSA provides authoritative, expert advice based on the latest intelligence that is accessible and easy to understand. NPSA works closely with the National Cyber Security Centre which provides advice on cyber security to businesses, other organisations and the public.

Visit the NPSA website

Other work

During much of the 20th century, subversion was a major concern for MI5. This threat diminished sharply following the end of the Cold War. We no longer undertake counter-subversion work, and would only resume doing so if our monitoring of emerging threats suggested an increase in the subversive threat.

We became involved in supporting police and law enforcement investigations of serious crime in 1996. This activity was suspended in 2006 so that we could concentrate on counter-terrorism. Work on serious crime is now carried out by the National Crime Agency (NCA)

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