Intercept: A Century of Signals Intelligence (2021)

GCHQ is the successor to the famous Bletchley Park wartime code-breaking organisation, it was set up following the First World War in 1919 and is the largest and most secretive intelligence organisation in the UK. During the WW2, it commanded more staff than MI5 and MI6 combined and has produced a number of intelligence triumphs, as well as notable failures. Since the end of the Cold War, it has played a pivotal role in shaping Britain's secret state. Still, little is known about it.