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. 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. 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. 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. Investigatory Powers Tribunal - IPT is the government body investigating complaints against the Intelligence Services, Police and public authorities relating to interception, surveillance and other conduct. Outlines independence and limitations. Centre for the Protection of National Infrastructure (CPNI) - Government authority that provides protective security advice to businesses and organisations across the national infrastructure. British Secret Intelligence Service - SIS comprises the foreign section, formerly MI6, with MI5 responsible for protecting the UK's internal security. Includes overview of work, history, relationship with other government bodies, FAQ and guidance for careers. Metropolitan Police Service: Special Operations - Provides a brief history and a list of responsibilities, including intelligence-gathering and operations on extremist political and terrorist activity. National Intelligence Machinery - Official document explaining how British security and intelligence agencies are organised and funded. 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.