Zircon was the codename for a British signals intelligence satellite, intended to be launched in 1988, before being cancelled.

During the Cold War GCHQ was heavily reliant on the NSA for communications interception from space. GCHQ therefore decided to produce a UK designed and built signals intelligence satellite, to be called Zircon. Its function was to intercept radio and other signals from the USSR, Europe and other areas. The satellite was to be launched on a NASA Space Shuttle under the guise of Skynet IV.

Zircon was cancelled on cost grounds in 1987. However, Duncan Campbell, an investigative journalist working for New Statesman magazine, published an article on Zircon. He discovered that the Zircon project had been hidden from Parliament, and estimated it was costing the government £100,000,000 a year. He went on to investigate Zircon in a BBC programme called "Secret Society" in 1986. Special Branch raids on the BBC and Campbell's home followed, and an injunction was released preventing the transmission of the programme. Despite this, the New Statesman published Campbell's article in January 1987. The television programme was delayed, and transmitted several years later.