The Government Communications Headquarters ( GCHQ ) is a British intelligence agency responsible for providing signals intelligence ( SIGINT ) and information assurance to the UK government and armed forces.

GCHQ is the responsibility of the UK Secretary of State for Foreign and Commonwealth Affairs, but it is not a part of the Foreign Office, and its Director ranks as a Permanent Secretary.

CESG ( originally Communications-Electronics Security Group ) is the branch of GCHQ which works to secure the communications and information systems of the government and critical parts of UK national infrastructure.

It is co-located with GCHQ for administrative purposes.

Ayios Nikolaos Station in Cyprus is run by the British Armed Forces for GCHQ.

The Communications-Electronics Security Group ( CESG ) of GCHQ provides assistance to government departments on their own communications security: CESG is the UK national technical authority for information assurance, including cryptography.

The JTLS is co-located with GCHQ for administrative purposes.

In this case, a prerogative Order in Council had been used by the prime minister ( who is the Minister for the Civil Service ) to ban trade union activities by civil servants working at GCHQ.

The following is a list of the heads of the operational heads of GCHQ and GCCS:

Clifford Cocks, an English mathematician working for the UK intelligence agency GCHQ, described an equivalent system in an internal document in 1973, but given the relatively expensive computers needed to implement it at the time, it was mostly considered a curiosity and, as far as is publicly known, was never deployed.

* July 15 – Geoffrey Prime, a GCHQ civil servant, is remanded in custody on charges under the Official Secrets Act 1911.

The Security Service, commonly known as MI5 ( Military Intelligence, Section 5 ), is the United Kingdom's internal counter-intelligence and security agency and is part of its core intelligence machinery alongside the Secret Intelligence Service ( SIS or MI6 ) focused on foreign threats, Government Communications Headquarters ( GCHQ ) and Defence Intelligence ( DI ).

The service is directed by the Joint Intelligence Committee for intelligence operational priorities and liaises with the SIS, GCHQ, DIS and a number of other bodies within the British government and industrial base.

However, after discovery of this document, the GCHQ official historian said: " I believe that this is indeed the same document that Balfour handed to Page.

Under the 1948 UKUSA agreement, CSEC's intelligence is shared with the United States National Security Agency ( NSA ), the British Government Communications Headquarters ( GCHQ ), the Australian Defence Signals Directorate ( DSD ) and New Zealand's Government Communications Security Bureau ( GCSB ).

Defence Intelligence is a key member of the United Kingdom Intelligence Community but differs from the agencies ( SIS, GCHQ, and the Security Service ) in that it is not a stand-alone organisation but is a constituent part of the Ministry of Defence ( MOD ).

Katharine Teresa Gun ( born Katharine Teresa Harwood in 1974 ) is a former translator for Government Communications Headquarters ( GCHQ ), a British intelligence agency.

During the Cold War there was a Composite Signals Organisation radio monitoring station in Helmsdale itself, the CSO is associated with GCHQ.

Red Pike is a classified United Kingdom government cipher, proposed for use by the National Health Service by GCHQ, but designed for a " broad range of applications in the British government ".

The Canadian officer who led the spying operation personally drove to GCHQ to deliver the fruits of the snooping: tape-recordings of the ministers ' communications over a three-week period.

The scheme was first published by Whitfield Diffie and Martin Hellman in 1976, although it was later alleged that it had been separately invented a few years earlier within GCHQ, the British signals intelligence agency, by Malcolm J. Williamson but was kept classified.

GCHQ was originally established after the First World War as the Government Code and Cypher School ( GCCS or GC & CS ), by which name it was known until 1946.

Since 1994, GCHQ activities have been subject to scrutiny by Parliament's Intelligence and Security Committee.

Post-Cold War, the aims of GCHQ were set out by the Intelligence Services Act 1994.

GCHQ gains its intelligence by monitoring a wide variety of communications and other electronic signals.

In 1997, it was publicly disclosed that asymmetric key algorithms were developed by James H. Ellis, Clifford Cocks, and Malcolm Williamson at the Government Communications Headquarters ( GCHQ ) in the UK in 1973.

Following the end of the war RSS HQ moved to Eastcote and was absorbed by the Government Communications Headquarters ( GCHQ ).

He opposed the privatisation of the Royal Ordnance Factories in 1984, in 1986 he criticised the Thatcher government for allowing the United States to bomb Libya from UK bases, and in 1987 he campaigned against the loss of trade union rights by workers at GCHQ.

Under this Act, since 1994, SIS and GCHQ activities have been subject to scrutiny by Parliament's Intelligence and Security Committee.

In a rare speech on the intelligence agencies, he praised the key role played by SIS and GCHQ in bringing Gaddafi ’ s 42-year dictatorship to an end, describing them as ‘ vital assets ’ with a ‘ fundamental and indispensable role ’ in keeping the nation safe.

In October 2005, it was revealed that an original typescript of the deciphered Zimmermann Telegram had recently been discovered by an unnamed historian who was researching and preparing an official history of the United Kingdom's Government Communications Headquarters ( GCHQ ).

In the British case code names were administered and controlled by ISSB ( The Inter-Services Security Board ) staffed by the War Office with the word list generated and randomised by GC & CS ( later GCHQ ).

In 1948 Good was recruited by the Government Communications Headquarters ( GCHQ ), successor to Bletchley Park.

The programme broadcast revelations by whistleblowers from both GCHQ, the government's electronic eavesdropping and surveillance headquarters, and from the Joint Intelligence Committee.

He held the post of Director of the Heilbronn Institute for Mathematical Research, a partnership between Bristol University and the British signals intelligence agency GCHQ, from its creation in 2005 until 2009.

* Sir David Pepper, Director of GCHQ from 2003-8

* Sir Eric Jones, Previous Director of GCHQ

He was Director of the Government Communications Headquarters ( GCHQ ) in Cheltenham from 1998 to 2003 and then served as Governor and Commander-in-Chief of Gibraltar from 2003 to 2006.

* Sir Brian Tovey, former Director of GCHQ

The Director of JTAC reports to the Director General of the Security Service ( commonly known as MI5 ), and directs a staff including personnel from the Security Service, Secret Intelligence Service ( commonly known as MI6 ), Government Communications Headquarters ( GCHQ ), Defence Intelligence Staff, Metropolitan Police Counter Terrorist Command and a further six government departments.

In addition several new private housing developments are currently in progress, the largest of these being on the site vacated by GCHQ, when it moved to its new site, also located in Hesters Way.