The Real Sir Humphrey
Three-part series by Michael Cockerell starts with the role played over the years by the most powerful unelected member of the government, the Cabinet Secretary.
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.
You are at the first episode