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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."

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. :

How We Operate


We work closely with a range of other agencies and organisations in seeking to counter threats to national security.

Security Service crest

Our work focuses on:

Investigating suspect individuals and organisations to obtain, collate, analyse and assess secret intelligence relating to the threats. This requires us to gather intelligence and manage information effectively.
Acting to counter the sources of threats, compiling evidence that enables us to bring suspects to justice.
Advising the Government and others to keep them informed of the threats and advises on the appropriate response, including protective security measures; and
Assisting other agencies, organisations and Government departments in combating threats. We contribute to the collective work of the UK's National Intelligence Machinery and form partnerships with other organisations in the UK and abroad.

Why we use secret intelligence

Although publicly available information can be helpful for background purposes, the best way to discover the intentions and actions of organisations and individuals posing a threat to national security is to obtain secret intelligence about their activities. Over time, we collate this information and seek to develop detailed knowledge of target organisations, their key personalities, infrastructure, intentions, plans, and capabilities.

If intelligence is worth recording we ensure that this is done accurately, clearly marking its origin and authenticity, and ensuring that it can be retrieved swiftly. If we assess that a particular threat needs to be investigated, then resources are deployed to obtain further intelligence. Assessments are continually adjusted in light of new intelligence or events.

This whole process of assessment and investigation helps us make decisions about counter action and protective measures. Our judgements of the scale of the various threats to national security and the distribution of our efforts in response are subject to validation by the Home Secretary and the external scrutiny of Parliament. We adjust our priorities according to the national requirements for intelligence, set by Government, drawn up by the Joint Intelligence Committee (JIC) and endorsed by Ministers.