GCHQ is the responsibility of the Foreign and Commonwealth Secretary. Its role is to provide the Government and military with sigint as required under the guidance of the JIC in support of government policies.
GCHQ was established in 1946 as the successor to the Government Code and Cipher School (GC&CS) which had been the government Sigint organisation since 1919, running Bletchley Park during WW II. Initially based on London in 1953 GCHQ was moved to the outskirts of Cheltenham, setting up two sites - Oakley and Benhall. It was not officially avowed until 1983. The following year GCHQ was the centre of a political row when the Conservative government of Margaret Thatcher prohibited its employees from joining a Trade Union, nominally in the interest of National Security. The ban was eventually lifted by the incoming Labour government in 1997.
Post Cold war the aims of GCHQ were set out by the Intelligence Services Act (1994). GCHQ is currently having a new 'doughnut' shaped HQ built at the Benhall site, where all its Cheltenham operations will be based from around 2003.
GCHQ gains its intelligence by monitoring a wide variety of communications and other electronic signals. For this a number of stations have been established in the UK and overseas which are run by the Composite Signals Organisation for GCHQ. The Composite Signals Organisation Station, at Morwenstowe in Bude, Cornwall is directly subordinate to GCHQ. The listening stations are at Cheltenham itself, GCHQ CSO Morwenstowe, GCHQ CSO Ascension Island, with the Americans at Menwith Hill, and the Columbia Annex (CANX)
In addition to sigint, GCHQ provides assistance to Government Departments on their own communications security. This task is given to the Communications Electronics Security Group (CESG) of GCHQ. CESG is the UK national authority for cryptography. CESG does not manufacture security equipment, but works with industry to ensure the availability of suitable products and services.