This new biography provides an account of the career of Reg Prentice, one of the most controversial yet neglected figures in modern British political history. Prentice remains the most high-profile politician to cross the floor of the House of Commons in the post-war period, and his defection was reflective of an important 'sea change' in British politics; the end of the post-war consensus and the beginnings of the Thatcher era. This book examines in detail the key events surrounding Prentice's transition from a front-line Labour politician, serving in the Wilson and Callaghan governments of 1974-79, through to his dramatic decision to join the Conservative Party of Margaret Thatcher. It specifically focuses on the shifting political climate in Britain during the 1970s, as the post-war settlement came under pressure from adverse economic conditions, militant trade unionism and an assertive New Left. Prentice's story provides an important case study on the crisis that afflicted social democracy, whilst highlighting the full extent of the divisions that emerged within the Labour Party and the underlying possibility of a realignment of British politics. This study represents a unique approach to political biography by offering students and academics an in-depth examination of the 1970s through the story of Prentice's political journey from left to right. It will be invaluable to anyone interested in the turbulent and transitional nature of British politics during a watershed period in recent history.