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 mediation scheme designed to solve the problem is becoming fraught, so MPs step up the campaign of political pressure on the Post Office. And Lee Castleton, a sub-postmaster from Bridlington, tells his story.

Presenter: Nick Wallis