During the course of the Twentieth Century, nineteen men and one woman - from Robert Cecil, Third Marquis of Salisbury to Tony Blair - have occupied the post of Prime Minister of the United Kingdom.

Dick Leonard is an historian, journalist and author and a former Labour MP. For many years he was Assistant Editor of The Economist, and headed their office in Brussels, where he was later also correspondent of The Observer. He also worked for the BBC, and contributed regularly to leading newspapers across the world. His publications include The Economist Guide to the European Union, Elections in Britain, A Century of Premiers: Salisbury to Blair; Nineteenth Century British Premiers: Pitt to Rosebery and Eighteenth Century British Premiers: Walpole to the Younger Pitt.