In this major study, Peter Hennessy explores the formal powers of the Prime Minister and how each incumbent has made the job his or her own. Drawing on unparalleled access to many of the leading figures, as well as the key civil servants and journalists of the period, he has built up a picture of the hidden nexus of influence and patronage surrounding the office. From recently declassified archival material he reconstructs, often for the first time, precise prime ministerial attitudes towards the key issues of peace and war. He concludes with a controversial assessment of the relative performance of each Prime Minister since 1945 and a new specification for the premiership as it enters its fourth century.