If anyone deserves the over-used epithet "national treasure", it is the man who has shed light on the eerie plans for national survival after war. In this expanded edition of Hennessy's masterwork, we learn that the Queen was long left in the dark about how government would continue when her kingdom was "largely a smoking and irradiated ruin".
The Prime Minister's World War III bunker was, until recently, a facility codenamed Turnstile, decorated with cricketing scenes and a missionary being boiled in a pot. Hennessy gives fewer details of its replacement, Pindar, below the MoD building in Whitehall.
A new chapter describes the Strangelove moment. "I could never, never have forgiven myself", said Callaghan, but Mrs Thatcher was "an intriguing puzzle".