Government Communications Headquarters
The U.K. Government Communications Headquarters (GCHQ) is Britain's signals intelligence and information assurance organization. Its functions are very similar to those of the U.S. National Security Agency, with which it works closely.
Under a still-classified "UKUSA Agreement", there is substantial sharing of signals intelligence collection and product among the Australian Defense Signals Directorate (DSD), Canadian Communications Security Establishment (CSE), New Zealand Government Communications Security Bureau (GCSB), and the United States National Security Agency (NSA). There may be another information-sharing agreement called ECHELON.  It is a direct descendant of the Second World War organization, the Government Code and Cipher School, which was responsible for the ULTRA cryptanalysis of the Enigma machine.
While the WWII GCCS was under the the Secret Intelligence Service (SIS), GCHQ reports to the Foreign Secretary and work closely with the SIS (commonly but incorrectly called MI6), Security Service (MI5) and military intelligence. The current director is Iain Lobban.
Before and during the Second World War, the organization was known as the Government Code and Cypher School (GCCS), based at Bletchley Park, which reported to the Secret Intelligence Service. Its major achievements included the ULTRA cryptanalysis of the German Enigma machine, although Polish and French cryptanalysis made important early breakthroughs. GCCS also obtained valuable intelligence through direction finding and traffic analysis by a division called the "Y Service".
Often called "Bletchley Park" after the WWII location, the current GCHQ main facility is actually in Cheltenham. There is, however, an "Enigma Tavern" in the town of Bletchley Park.
The British also developed an effective controlled dissemination mechanism for this sensitive intelligence, called Special Liaison Officers under F.W. Winterbotham. This was the ancestor of many of today's compartmented control systems; while that article is U.S.-specific, many of the "COMINT Channels Only" procedures are shared the UKUSA members.
- European Parliament Report on ECHELON, 2001. Retrieved on 2006-08-14