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 we meet the man who led that fight; the UK's Erin Brokovich, Alan Bates, founder of the Justice For Subpostmasters Alliance. A man who faced seemingly insurmountable odds in trying to take on a national institution but who refused to be cowed.

Presenter: Nick Wallis