The British political system, though often criticized, has been the model and the inspiration for many national governments world-wide. It is the center of controversial debate within Britain itself. Yet over the 130 years since Bagehot wrote his English Constitution, no historian has investigated in depth how it has evolved in all its dimensions, and few political scientists have looked further back than the Second World War. This is the first book to provide a detailed explanation of how the British political system came to acquire the form it has today.