Dave McDonnell becomes the most important witness of the second phase of the Post Office Horizon IT inquiry so far by explaining in detail exactly how the Horizon system did not and would not work, how he told his bosses at Fujitsu and how they ignored his advice, sidelined him and rolled out a financial system into the Post Office estate, leaving it to wreak havoc on Subpostmasters. Nick and Rebecca trawl through two days of pretty intense evidence to bring you the audio highlights.