Finally the 1946 UKUSA Agreement is public. It created a world-wide network of listening posts run by the US National Security Agency (NSA) and the UK's Government Communications Headquarters (GCHQ), which endures today. In 1948 Canada joined and in 1956 Australia and New Zealand too - though they have always been junior partners. The latter, being Commonwealth countries, provide an important geographical spread as does GCHQ in Cyprus (which monitors the Middle East).
An extended UK/USA-run surveillance network known as ECHELON emerged in the 1960s. Although created for the Cold War era it has has adapted to new roles under the "war on terrorism". GCHQ, based in Cheltenham, employs 5,500 people and is significantly larger than MI5 (internal security) and MI6 (external).