The book addresses questions important to aspiring politicians as well as scholars, including: What accounts for the short tenure of most Japanese prime ministers? Does comparison with Japan explain the rapid turnover in British prime ministers since 2016? How is the influence of party factions on prime ministerial power evolving in Japan? Are British political parties more factional than commonly acknowledged? And how do changes in media technology affect leadership opportunities and constraints? Thebook draws on the author’s experience as a political researcher in both the British and Japanese parliaments and on interviews with over 40 politicians and political journalists working in both countries.