The Post Office Horizon Scandal has been called the widest miscarriage of justice in modern British history, with the number of former Sub Postmasters whose convictions have been overturned now over 60. Those who suffered prosecution or financial ruin due to errors on the Post Office's Horizon computer system want answers. How could this have happened? Who is responsible?

Continuing the series that has helped expose the scandal since 2020, Nick Wallis draws on interviews, documents and the extraordinary revelations spilling out of the ongoing public inquiry. For the first time, the public is getting real insight into what was really going on inside the Post Office.

In Episode 17, Nick explores how senior Post Office lawyers and managers reacted in 2013 to the biggest challenge to the Horizon system yet. After MPs forced an independent investigation which identified bugs in Horizon, the Post Office publicly backed their computer system and reaffirmed their faith in the prosecutions they had conducted. But behind the scenes, all hell was breaking loose.

Presenter: Nick WallisProducer: Robert NicholsonSound Design and Mixing: Arlie AdlingtonExecutive Producer: Will Yates

A Whistledown production for BBC Radio 4