GCHQ Fact File
* Currently GCHQ employs over 5,000 people.
* The Cheltenham building was opened in 2003.
* GCHQ was previously known as Government Code and Cipher School.
* GC&CS were responsible for communications and decrypting messages. The most famous example of this was when the British decrypted the ENIGMA Machine messages in the Second World War.
* GCHQ has two missions - signals intelligence (sigint) and information assurance.
* Sigint works to provide the government with information to help stop terrorism and serious crime.
* Information assurance works to protect British infrastructure, making sure critical networks (water, communications, power) are safe from hackers and viruses.
* The linguistics team work in 40 languages and dialects every day.
* The specialist skills of the workforce range from cyber security specialists, communication engineering, mathematics and analysis.
* The building is made up of three separate structures which combined are the same size as the old Wembley stadium.
* The building has 13,000 square metres of glass - equivalent to double-glazing for 10% of the houses in Cheltenham.
Source: GCHQ website
For the first time a former director of GCHQ talks about his time working in the UK government's intelligence service in Cheltenham.
Sir Arthur Bonsall is a former director of GCHQ who lived a life in the shadows for almost 40 years.
Inside Out's Steve Knibbs has been allowed extremely rare access to the GCHQ building in Cheltenham to speak with him.
Watch the video feature on the BBC News website.
- Mary Rhodes
- Series Editor
- Rachel Bowering