In the great revolutionary year of 1968, Tony Benn was a respectable Labour minister in his forties, and he was restless. While new social movements were shaking up Britain and much of the world, Westminster politics seemed stuck. It was time, he decided, for a different approach.

Over the next half century, the radicalized Benn helped forge a new left in Britain. He was joined by four other politicians, who would become comrades, collaborators and rivals: Ken Livingstone, John McDonnell, Diane Abbott and Jeremy Corbyn.

For Andy Beckett, the story of these admired and loathed political explorers - both their sudden breakthroughs and long stretches in the wilderness - is the untold story of British politics in modern times. As he reveals, their project to create a radically more equal, liberal and democratic Britain has been much more influential than electoral history might suggest, and can be seen from the shape of our city life to the causes of our culture wars.

For their many detractors, this influence was and remains dangerous: a form of extremism that must be stamped out. But as these five searchers believed, in politics there is no total victory - nor total defeat.