The British Post Office scandal, also called the Horizon IT scandal, involved the Post Office pursuing thousands of innocent subpostmasters for apparent financial shortfalls caused by faults in Horizon, an accounting software system developed by Fujitsu. Between 1999 and 2015, more than 900 subpostmasters were convicted of theft, fraud and false accounting based on faulty Horizon data, with about 700 of these prosecutions carried out by the Post Office. Other subpostmasters were prosecuted but not convicted, forced to cover shortfalls—caused by Horizon—with their own money, or had their contracts terminated. The court cases, criminal convictions, imprisonments, loss of livelihoods and homes, debts, and bankruptcies led to stress, illness, family breakdowns and at least four suicides. In 2024, Prime Minister Rishi Sunak described the scandal as one of the greatest miscarriages of justice in British history.
Although many subpostmasters had reported problems with the new software, and Fujitsu was aware that Horizon contained software bugs as early as 1999, the Post Office insisted that Horizon was robust and failed to disclose knowledge of the faults in the system during criminal and civil cases. In 2009, Computer Weekly broke the story about problems with Horizon, and the former subpostmaster Alan Bates launched the Justice for Subpostmasters Alliance (JFSA). In 2012, following pressure from campaigners and Members of Parliament, the Post Office appointed forensic accountants from the firm Second Sight to conduct an investigation into Horizon. With Second Sight and the JFSA, the Post Office set up a mediation scheme for subpostmasters but terminated it after 18 months.
In 2017, 555 subpostmasters led by Bates brought a group action against the Post Office in the High Court. In 2019, the judge ruled that the subpostmasters' contracts were unfair, and that Horizon "contained bugs, errors and defects". The case was settled for £58 million, leaving the claimants with £12 million after legal costs. The judge's rulings led to subpostmasters challenging their convictions in the courts and the government setting up an independent inquiry in 2020. The Post Office Horizon IT Inquiry was converted into a statutory public inquiry the following year. The public inquiry is ongoing and the Metropolitan Police are investigating personnel from the Post Office and Fujitsu.
Courts began to quash the subpostmasters' convictions in December 2020. By February 2024, 100 of the convictions had been overturned. Those wrongfully convicted became eligible for compensation, as did more than 2,750 subpostmasters who had been affected by the scandal but not convicted. The final cost of compensation is expected to exceed £1 billion. In January 2024, ITV broadcast a television drama, Mr Bates vs The Post Office, which made the scandal a major news story and political issue. In May 2024, the UK Parliament passed a law overturning the convictions of subpostmasters in England, Wales and Northern Ireland. Scotland passed a similar law the same month.