After the introduction of a new computer system in the early 2000s, the Post Office began using its data to accuse sub-postmasters of falsifying accounts and stealing money. Many were fired and financially ruined; others were prosecuted and even put behind bars. In this ten-part series, journalist Nick Wallis, gets right to the heart of the story, as he talks to those whose lives were shattered and follows the twists and turns of a David and Goliath battle as the sub-postmasters tried to fight back. Today, the Post Office is standing firm in the face of political pressure, and Nick explores an explosive intervention from an unlikely source - the sub-postmasters' own union. Presenter: Nick Wallis Producer: Robert Nicholson Executive Producer: David Prest With Sound Design from Emma Barnaby and Story Editing from Alexis Hood. A Whistledown production for BBC Radio 4