The Home Secretary is accountable to Parliament for the activities of the Security Service.
The Service, unlike the police, has no powers of arrest or detention. It has no intrinsic powers of search or seizure of property. Its functions are governed by the Security Service Act 1989. That Act together with the Intelligence Services Act 1994 and Regulation of Investigatory Powers Act 2000 provides a firm statutory framework within which the Security Service operates. All work of the Service is undertaken in accordance with the law, including the European Convention of Human Rights as incorporated into UK law by the Human Rights Act 1998.
Authorisations for operational activities are subject to independent oversight by the Intelligence Services, or Interception, Commissioner to ensure that any conduct is lawful, and proportionate to what is sought to be achieved by that conduct.
Security Service operational guidance is kept under regular review. Any change to that guidance is submitted to the Home Secretary for approval.