The Horizon Error Horizon was developed by Japanese software company Fujitsu with features intended to handle transactions, stocktaking and accounting. A 2003 document published by Fujitsu described the system as helping the Post Office and its branches to “become more efficient and improve their services by reducing customers’ waiting time, simplifying procedures, and computerising traditional paperwork”. The system was rolled out in 1999 and its use continued well into the 2000s, with a full 11,500 branches making use of it by 2013. At this time, around eight million transactions were being processed by Horizon every day. However, cracks in the system had begun to show as early as its debut year. Sub-postmasters who adopted the system reported unnerving errors, often involving significant quantities of money. Two of the most significant of these became to be known as the Callendar Square Bug and the Dalmellington Bug, the first of which generated false duplicate financial transactions that were considered the responsibility of the user rather than the database, and the latter of which caused the system to apparently lock up while users acknowledged receipt of a cash consignment, prompting said users to hit a key multiple times while unknowingly accepting responsibility for new consignments each time. Neither issue became public knowledge for more than a decade after Horizon’s introduction across Post Office branches. On the back of these and numerous other bugs, the system began to report financial shortfalls from Post Office branches, which were again placed at the feet of the sub-postmasters who had taken Horizon on board. Some of the shortfalls ran into the thousands of pounds. Some sub-postmasters attempted to use their own money to bridge the gap, in some cases remortgaging their own homes, to little effect. The Post Office rejected claims that Horizon itself was at fault for the reported shortfalls, arguing repeatedly in statements that the system was “robust”. Miscarriage of Justice Sub-postmasters who were unable or unwilling to clear the deficits reported by Horizon were prosecuted by the Post Office. Claims of theft, fraud and false accounting were most common among these, with the majority of cases resting on IT evidence alone. In total, it is believed that between 2000 and 2014, 736 sub-postmasters were falsely convicted as part of the scandal; an average of one per week. The impact of these false sentences has still not fully come to light, but many sub-postmasters were imprisoned following their convictions, while others were financially or reputationally ruined. Several reported the loss of subordinates’ jobs and the breakup of families in the wake of the artificially incurred losses. One victim is known to have committed suicide. The debilitating bugs at the centre of the scandal were finally brought to light in the December 2019 Bates & Others v Post Office Ltd group litigation on behalf of more than 500 sub-postmasters prosecuted with IT evidence. Mr Justice Fraser found in his ruling on the lawsuit that software errors and defects in the Horizon system did exist and were sufficient to undermine its reliability in accurately processing and determining transactions, which had happened on multiple occasions. 36 LAWYER MONTHLY AUGUST 2023
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