In 1999, the Post Office introduced a brand-new way of cataloguing payments: the Horizon IT system. It was intended to be a way to modernise the organisation, moving it from paper-based records into the upcoming 21st century.What unfolded instead was a disaster. The Horizon IT system was faulty, prone to glitches which incorrectly exhibited shortfalls of cash that were blamed on the subpostmasters in charge of their branches, leading to twenty years of legal disputes, hundreds of wrongful convictions and untold lives destroyed.Now the whole sorry affair is being turned into an ITV drama, Mr Bates vs The Post Office, airing on January 1.