For a hundred years GCHQ – Government Communications Headquarters – has been at the forefront of British secret statecraft. Born out of the need to support military operations in the First World War, and fought over ever since, today it is the UK’s biggest intelligence, security and cyber agency and a powerful tool of the British state.

Famed primarily for its codebreaking achievements at Bletchley Park against the Enigma ciphers in the Second World War, GCHQ has intercepted, interpreted and disrupted the information networks of Britain’s enemies for a century. In November 2020 John Ferris, official historian of GCHQ, came to Intelligence Squared to lift the lid on the least understood of the British intelligence services. 

Drawing on the unprecedented access he was given to documents in GCHQ’s archive, many of them hitherto classified, Ferris authoritatively explained the history of one of the world’s most powerful intelligence agencies. Many major contemporary conflicts – between Russia and the West, between Arab nations and Israel, between state security and terrorism – become fully explicable only in the light of the secret intelligence record. In conversation with Shashank Joshi, defence editor at The Economist, Ferris delved into the past and peer into the future of the nation’s security.