The Zircon affair was an incident in 1986 and 1987 caused by the planned broadcast on the BBC of a television programme about the ultimately cancelled Zircon signals intelligence satellite, as part of the six-part Secret Society series. It raised many important issues in the British constitution, particularly concerning parliamentary privilege and "gagging orders".
In November 1985 the Scottish investigative journalist Duncan Campbell was commissioned by BBC Scotland to present and research a six part, half-hour documentary series called Secret Society, produced by Brian Barr. GCHQ became aware that a BBC Scotland crew were filming at RAF Menwith Hill, and when Campbell interviewed the former Chief Scientific Adviser to the Ministry of Defence Ronald Mason in August 1986 he mentioned the Zircon Project (regarded as "exceptionally secret").
Campbell had planned to use an episode of Secret Society to reveal the existence of Zircon, but found while researching the programme in mid-1986 that the head of the Public Accounts Committee (PAC), Robert Sheldon, knew nothing of the project. The Public Accounts Committee is a select committee of the House of Commons, responsible for overseeing government expenditures. It had been agreed between Parliament and the British government that expensive military projects should be subject to scrutiny by the committee, and Campbell felt that Sheldon's ignorance of the Zircon project was evidence of the violation of this agreement. The concealment of Zircon, which had an estimated cost of £500 million (equivalent to £1.6 billion in 2021), from the committee mirrored the parliamentary secrecy over a previous defence project, the Chevaline programme to enhance the Polaris nuclear missile. The previous head of the PAC, Lord Barnett, had been recently appointed the BBC Vice-Chairman. Barnett had withdrawn from a planned interview with Campbell for the programme after his BBC appointment, upset at the nature of the questioning that Sheldon had faced, who had accused Campbell of setting him up.