Centre for the Protection of National Infrastructure (CPNI)
- Government authority that provides protective security advice to businesses and organisations across the national infrastructure.
- http://www.cpni.gov.uk/

National Intelligence Machinery
- Official document explaining how British security and intelligence agencies are organised and funded.
- http://www.archive.official-documents.co.uk/document/caboff/nim/0114301808.pdf

Cabinet Office - Intelligence and Security Committee
- Offers news, list of committee members, and links to annual reports and other official publications.
- http://www.cabinetoffice.gov.uk/intelligence/

Investigatory Powers Tribunal (IPT)
- Official independent tribunal investigating complaints against the Intelligence Services, Police and public authorities relating to interception, surveillance and other conduct.
- http://www.ipt-uk.com

Scottish Executive - Guidelines on Special Branch Work in the United Kingdom
- Official report describes the roles and functions of this intelligence and policing service at national, regional and local levels.
- http://www.scotland.gov.uk/library5/justice/sbwuk.pdf

Metropolitan Police Service - Special Branch
- Provides a brief history and a list of responsibilities, including intelligence-gathering and operations on extremist political and terrorist activity.
- http://www.met.police.uk/so/special_branch.htm

Wikipedia - MI5
- Hyperlinked encyclopaedia entry provides the history of the Security Service, responsible for protecting British Parliamentary democracy and economic interests, and fighting serious crime.
- http://en.wikipedia.org/wiki/MI5

Wikipedia - Secret Intelligence Service
- Hyperlinked encyclopaedia article about MI6 (Her Majesty's Secret Service) provides a history of its role beginning with the First World War. With list of directors.
- http://en.wikipedia.org/wiki/Secret_Intelligence_Service

Foreign & Commonwealth Office - Secret Intelligence Service (SIS)
- Describes MI6, a Crown Service responsible for obtaining secret information and conducting operations in support of the UK’s foreign policy objectives, and to counter threats to UK interests worldwide.
- http://www.fco.gov.uk/servlet/Front?pagename=OpenMarket/Xcelerate/ShowPage&c=Page&cid=1059736061019

Office of Surveillance Commissioners
- Provides information about the roles and responsibilities of those who authorise and conduct covert surveillance operations and covert human intelligence sources.
- http://www.surveillancecommissioners.gov.uk/

GCHQ
- Official site of the UK Government Communications Headquarters which is the centre for Her Majesty's Government's Signal Intelligence (SIGINT) activities. Includes details of current job vacancies and an online quiz for potential applicants.
- http://www.gchq.gov.uk/

MI5 The Security Service
- Provides information on the current major threats to UK security and expert security advice designed to help businesses and organisations protect against them.
- http://www.mi5.gov.uk/