Watch The Great Offices of State online: Episode 3 The Secret Treasury

The Treasury is the oldest and most secretive of the three. Cockerell's film recounts the many battles Chancellors have fought over the years with their top officials and it shows how often the Treasury has been locked in conflict with Number 10. He blends fresh filming with rare and unseen archive, and features candid interviews with the current Chancellor Alastair Darling, many of his predecessors and their normally camera-shy mandarins. The programme shows how Treasury officials see themselves as the Whitehall elite, brighter and quicker than other civil servants, whereas critics claim they are congenitally cautious and nerdy. Successive prime ministers have sought to combat what they call 'the dead hand of the Treasury', but a senior mandarin claims that over the years the Treasury has discovered a hundred different ways of saying no.

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