In his look at the Home Office - the ministry of law and order, immigration, MI5 and counter-terrorism - Cockerell blends fresh access filming with formerly unseen and rare archive, and interviews with present and past home secretaries and their senior officials.

Cameras follow Alan Johnson from the moment he became the sixth home secretary in twelve years, after the resignation of Jacqui Smith. Johnson is briefed by the Home Office spin doctor about what to say to story-hungry journalists waiting for him. 'The Home Office's job is to confront human evil', says one mandarin, 'but every person in the pub has his own view of how to do it and is his or her own home secretary'.

The Foreign Office is the grandest of the three, built in Victorian times to impress foreigners when the British lion still strutted the globe. How the Foreign Office has sought over the years to come to terms with Britain's reduced status in the world makes an often tragicomic tale.

Cockerell blends fresh access filming, rare and previously unseen archive and interviews with past and present foreign secretaries and their normally camera-shy senior officials. The film tells of the many behind-the-scenes battles in the FO between its mandarins and ministers and against 10 Downing Street.

Successive prime ministers have regarded the Foreign Office as temperamentally inclined to kow-tow to foreigners and have sought to be their own foreign secretaries - often with disastrous consequences. The film also explores the always-uneasy relationship between the FO and its offshoot, Britain's spy agency, MI6.

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 former 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.