MI5 - Security Service

What we do

The Security Service is responsible for "protecting the UK against threats to national security from espionage, terrorism and sabotage, from the activities of agents of foreign powers, and from actions intended to overthrow or undermine parliamentary democracy by political, industrial or violent means."

Security Service crest

See "Protecting National Security" for more information on what this means in practice.

We also provide security advice to a range of organisations in the public and private sectors, and work against the proliferation of weapons of mass destruction. We have also contributed to the fight against serious crime, though our work in this area is currently suspended.

Our statement of objectives and values explains the Service's responsibilities in more detail, and outlines the civic values that we follow in performing our duties.

As our resources are limited, it is essential that we use them effectively so that we can achieve the greatest impact against the most serious threats. See Major Areas of Work for more details on how we deploy our resources and what we are doing to combat specific threats.

The role of the Security Service is defined by law in the Security Service Act 1989 opens in a new window. See Statutory Basis for more information on what the law says about the Security Service's functions and relationship with the Government.

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:

Key points

Main responsibilities:

  • Counter terrorism
  • Counter espionage
  • Counter proliferation
  • Role is defined in Security Service Act 1989.

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