State surveillance in the United Kingdom has formed part of the public consciousness since the 19th century. The postal espionage crisis of 1844 sparked the first panic over the privacy of citizens. However, in the 20th century, electronic surveillance capabilities grew out of wartime signal intelligence and pioneering code breaking. In 1946, the Government Communications Headquarters (GCHQ) was formed. The United Kingdom and the United States signed the bilateral UKUSA Agreement in 1948. It was later broadened to include Canada, Australia and New Zealand, as well as cooperation with several "third-party" nations. This became the cornerstone of Western intelligence gathering and the "Special Relationship" between the UK and the USA.