The Horizon scandal is regarded as the most extensive miscarriage of justice in UK history.

From 1999 to 2015, the Post Office pursued hundreds of branch operators for alleged theft and fraud, despite being aware of known faults in the Horizon software.

Approximately 3,500 post office operators were wrongly accused, with over 900 facing prosecution, leading to significant injustices.

Neil McCausland, former interim chair of the Post Office from 2011 to 2016, criticized the organization's management and the Horizon IT system during a public inquiry into the scandal.

McCausland described the Post Office as 'badly run and messy' and highlighted the outdated and poorly maintained IT infrastructure.

He noted that the Horizon accounting software, developed by Fujitsu, was at least 15 years old and typically should have been replaced after a decade.

During his first board meeting discussing Horizon, McCausland was assured by a director from Royal Mail Group that the system was reliable, despite previous legal claims about its integrity being weak.

Despite acknowledging the system's shortcomings, McCausland stated that he was led to believe the data integrity of Horizon was sound and received positive audits regarding its performance.