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MI5 works within a strict framework of legislation and oversight to ensure our investigative powers are only used where it is necessary and proportionate to do so. Our work is subject to rigorous scrutiny: by the Home Secretary, who personally signs warrants for our most intrusive activity; by Parliament, in the Intelligence and Security Committee; by two independent commissioners, both former senior judges; and by the Investigatory Powers Tribunal.

The Investigatory Powers Act will change these oversight arrangements and aims to modernise the legal framework within which the intelligence agencies work.

Role and responsibilities

The statutory basis under which MI5 operates is set out in the Security Service Act 1989. The Act sets out our functions and gives some examples of the nature and range of threats that we are responsible for countering.

In summary our functions are:

  • to protect national security 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;
  • to safeguard the economic well-being of the UK against threats posed by the actions or intentions of persons outside the British Isles; and
  • to act in support of the activities of the police forces and other law enforcement agencies in the prevention and detection of serious crime. However, since the establishment of the Serious Organised Crime Agency and subsequently the National Crime Agency, MI5 has suspended work on serious crime in order to concentrate more resources on counter terrorism.

In a democracy, a domestic security service must be apolitical and accountable. The Act places us under the authority of a Secretary of State, in practice the Home Secretary, who is accountable to Parliament for the work of MI5.

The Act also sets out the Director General's responsibilities in law for ensuring that we do not act to further the interests of any political party. Our role is to protect democracy, not to influence its course. The government of the day cannot instruct MI5 to perform any action for party political reasons.

The right to respect for private and family life

Article 8 of the European Convention on Human Rights (ECHR) asserts the right to respect for private and family life, home and correspondence. It states that public authorities should not interfere with this right, except in specific circumstances, and this obligation is embodied in the UK through the Human Rights Act 1998.

MI5’s functions are recognised in Article 8 as providing a legitimate basis, in appropriate cases, for interference with an individual’s right to respect for their privacy. Leander v Sweden (1987) established that a state can pursue these functions through a security service that has a clear legal basis.

The state should also ensure that there are adequate and effective guarantees against abuse. The Regulation of Investigatory Powers Act 2000 (RIPA) established mechanisms for the oversight and control of MI5’s activities.

Intelligence gathering

RIPA provides a legal framework for the use of covert surveillance, covert human intelligence sources (“agents” or “CHIS”), the interception of communications, and the acquisition, disclosure and retention of communications data.

All intelligence gathering activities that fall into these categories must, under RIPA, be authorised by designated persons within MI5. These individuals must agree that the action is necessary and proportionate to the aims of the investigation, and that the information cannot be obtained using less intrusive methods. Authorisations must be recorded, and made available to independent commissioners appointed under the terms of RIPA to ensure intelligence gathering is proportionate and not used excessively or inappropriately.

Interception of communications and intrusive surveillance also require the authority of a warrant signed by a Secretary of State, usually the Home Secretary. In most cases, intrusive surveillance will also require a property warrant under the Intelligence Services Act 1994 (authorised by a Secretary of State), to authorise any interference with an individual’s property that is necessary to install a surveillance device.

Oversight of intelligence gathering

RIPA established three oversight bodies.

The Interception of Communications Commissioner’s Office (IoCCO) is responsible for reviewing warrants issued for the interception of communications, and for overseeing arrangements for gaining access to communications data.

The Intelligence Services Commissioner’s Office reviews warrants issued to authorise intrusive surveillance and interference with property. The commissioner is also responsible for reviewing internal authorisations for directed surveillance and the use of covert human intelligence sources to make sure MI5 is acting in accordance with the law.

RIPA also created the Investigatory Powers Tribunal (IPT). The IPT is a court which investigates complaints of unlawful use of covert techniques, and claims that intelligence agencies or other public authorities have infringed individuals’ right to privacy or their wider human rights. For more information, see the IPT’s website which contains information on how to lodge a complaint as well as recent decisions made by the IPT.

Summary of requirements for intelligence gathering activities


Authorisation required?

Warrant required?

Reviewed by

Communications data

Data about communications but not the content of the communication, such as the date, time and duration of a phone call.



Interception of Communications Commissioner

Interception of communications

Access to communications content, such as listening to a phone call or reading an email or letter.



Interception of Communications Commissioner

Directed surveillance

Covert monitoring of an individual’s movements, conversations and activities.



Intelligence Services Commissioner

Intrusive surveillance

Covert monitoring of an individual within their home or a private vehicle.


Yes (plus a property warrant in most cases)

Intelligence Services Commissioner

Use of covert human intelligence sources

Tasking an agent to obtain or provide access to information through their relationships with other people.



Intelligence Services Commissioner

Equipment interference

Obtaining access to the contents of stored communications or information on computers or other devices.



Intelligence Services Commissioner

Bulk personal data

Datasets containing information about a large number of people which can be accessed in a targeted way to identify or find information about subjects of interest.


Expected (the Investigatory Powers Act provides judicial commissioner approval of warrants issued by the Secretary of State.

Intelligence Services Commissioner


Commercial data retention

The Data Retention and Investigatory Powers Act 2014 confirms that companies can be required to retain certain types of communications data for up to 12 months. It also clarifies that companies providing communications services to UK customers should comply with requests for data made under RIPA regardless of where they provide the service from.

Access to information

Three pieces of legislation define the individual's right to access information held about them within the public sector: the Data Protection Act 2018 (DPA), the Freedom of Information Act 2000 (FOIA) and the Environmental Information Regulations (EIR). In addition to this, most public sector bodies which process personal data are subject to Regulation 2016/679 of the European Parliament and of the Council of 27 April 2016 (known as the General Data Protection Regulation, or GDPR). However, MI5 is not subject to the GDPR and processes personal data pursuant to Part 4 of the Data Protection Act 2018.

For more information about this, see Access to information.

Police powers and restrictive measures

The Terrorism Act 2000, Anti-Terrorism, Crime and Security Act 2001, Terrorism Act 2006 and Counter-Terrorism Act 2008 have defined and expanded the range of criminal activities related to terrorism, and police powers to deal with them.

The Terrorism Prevention and Investigation Measures (TPIMs) Act 2011 introduced TPIMs to reduce the risk from people believed to be engaged in terrorism-related activity who cannot be prosecuted or deported. The restrictive measures are more tightly proscribed than those previously available under control orders, which TPIMs replace.

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