Whistleblower testifies in Post Office scandal

Whistleblower Richard Roll revealed to BBC Panorama in 2015 that staff from Fujitsu could secretly alter sub-postmaster's accounts on the Post Office's Horizon computer system.

His testimony marked a turning point for sub-postmasters fighting to prove their innocence after the Post Office held them responsible for financial shortfalls.

The Post Office staged a campaign of threats and misinformation in a bid to halt or delay broadcast of the interview with Mr Roll, including smearing sub-postmasters and sending legal threats to Panorama's expert sources.