Illustration by Anthony Gerace This is a story about four left-wing Labour politicians – John McDonnell, Jeremy Corbyn, Ken Livingstone and Diane Abbott – and how they carried forward the cultural revolution of 1968. Inspired and guided by the older Tony Benn, the fifth “searcher” of the title, they single-mindedly enlivened a moribund London Labour politics and transformed the political culture of the capital as it emerged from its postwar decline. In their comradely, disputatious and occasionally angry relationships with one another they shared a political heritage in Benn’s democratic socialism. In 1981 his bid for the deputy leadership had...