The Security Service Act 1989 (c 5) is an Act of the United Kingdom Parliament.
The Act established the legal basis of the UK Security Service for the first time. The first section begins, "There shall continue to be a Security Service ..".
The first section defines the function of the Service as
the protection of national security and, in particular, its protection against threats 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.
In the next paragraph it adds the further function, "to safeguard the economic well-being of the United Kingdom against threats posed by the actions or intentions of persons outside the British Islands."