He is the real life Sir Humphrey from Yes Prime Minister, who rules the civil service from Whitehall's least understood ministry, the Cabinet Office. Mixing rare archive with candid interviews, the programme tells the story of the many battles for power between Britain's top civil servant and their prime ministers.

Michael Cockerell reveals what life has really been like over the years in 10 Downing Street. Insiders talk candidly about the constant battles and the tragicomic events behind the famous black door. The film shows what an unlikely place No10 is to run a government from.

Exploring the hidden power houses of Whitehall - the cabinet minister's private office.