Britain's Post Office Prosecuted Over 900 Sub-Postmasters Using Software It Knew Was Broken. Fujitsu Still Won New Government Contracts.

Between 1999 and 2015, Britain's Post Office prosecuted more than 900 of its own sub-postmasters for theft, false accounting and fraud, using shortfall figures generated by a piece of accounting software called Horizon. The Post Office had the legal power to do this itself, as a private prosecutor, without involving the Crown Prosecution Service. Fujitsu, the company that built Horizon, later told a parliamentary committee that bugs in the system had been "well known to all parties" from the very start of the rollout.

The Post Office kept prosecuting people on Horizon's numbers for another two decades after those bugs were first logged internally. It did not formally accept the software was flawed until it lost a civil case in the High Court in 2019. Convictions did not start being quashed en masse until 2021, and Parliament did not pass a law overturning them wholesale until 2024 — after a television drama, not a court judgment, made the scandal impossible for the public to ignore.

A Fault Line Nobody Told the Courts About

Horizon went live across Post Office branches from 1999, replacing paper ledgers with a Fujitsu-built accounting system that could, without warning, generate phantom shortfalls — discrepancies between what a branch's till actually held and what the software said it should hold. Fujitsu maintained an internal log of these problems, and its own European head, Paul Patterson, told the Commons Business and Trade Committee in January 2024 that bugs, errors and defects in Horizon were "well known to all parties" from day one, according to Bloomberg's reporting on his testimony.

The Post Office's public position throughout this period was that Horizon's data was reliable and that a shortfall on a branch's books meant money was actually missing. Sub-postmasters who said the software was wrong were routinely told they were the only ones reporting problems. The statutory inquiry chaired by Sir Wyn Williams later found that a number of Post Office employees, senior and otherwise, knew or should have known that the system was capable of error, while the organisation maintained what the inquiry's own findings characterised as the fiction that its data was always accurate.

Nine Hundred Prosecutions, One Private Prosecutor

The Post Office prosecuted roughly 700 sub-postmasters itself between 1999 and 2015, using powers available to it under the Prosecution of Offences Act 1985 — the same general right to bring a private prosecution that any individual or company holds, but backed by investigators with access to the Police National Computer and powers to pursue confiscation proceedings. A further 283 people were prosecuted by other bodies, including the Crown Prosecution Service, relying on evidence the Post Office supplied, bringing the total to more than 900 prosecutions built on Horizon data.

Many of those convicted were sent to prison; others were bankrupted by legal costs or forced to repay money that was never actually missing. The Criminal Cases Review Commission has since described the resulting miscarriage of justice as the largest in British legal history by number of cases.

Five Names Behind the Numbers

• Lee Castleton, a sub-postmaster in Bridlington, was pursued by the Post Office through the civil courts over a disputed shortfall of £25,000; the Post Office spent roughly £320,000 suing him, and he was made bankrupt after losing the case while representing himself, according to BBC reporting.
• Seema Misra was convicted of theft in 2010 and sentenced to 15 months in prison while eight weeks pregnant; her conviction was quashed by the Court of Appeal in 2021.
• Jo Hamilton, a former sub-postmaster in Hampshire, was told in 2005 that she owed the Post Office £36,000; she pleaded guilty to false accounting after being told the theft charge would otherwise proceed, despite the Post Office having no evidence of theft.
• Martin Griffiths, a sub-postmaster in Ellesmere Port accused of a £100,000 shortfall, took his own life in 2013 at the age of 59; the statutory inquiry has named his death as one it examined for a link to the scandal.
• The public inquiry told the BBC and other outlets it could not rule out a causal connection between the Horizon scandal and 13 deaths by suicide, and heard that 59 people who gave evidence had contemplated suicide, of whom 10 had attempted it.

The Judgment That Called the Fiction by Its Name

Alan Bates, a former sub-postmaster who had been trying to raise the alarm since the early 2000s, led a group litigation of 555 claimants against the Post Office in the High Court. In a ruling handed down in March 2019, Mr Justice Fraser found that the version of Horizon used between 2000 and 2010 "was not remotely robust," and that bugs, errors or defects had caused discrepancies at branches on numerous occasions — directly contradicting nearly two decades of the Post Office's position in court and in individual prosecutions.

The Post Office settled the group litigation in December 2019 for roughly £58 million. Of that, about £46 million went to legal costs, leaving the 555 claimants to divide approximately £12 million between them — an average of around £20,000 each, a fraction of the losses many had suffered.

A Four-Night Drama Did What a Court Order Couldn't

The 2019 judgment established the legal facts. It did not trigger mass exoneration. That took a four-part ITV dramatisation, "Mr Bates vs The Post Office," which aired on consecutive nights from 1 to 4 January 2024 and drew 9.2 million viewers for its first episode — ITV's best-performing new drama in years. Within days, the case dominated national news and Parliament.

On 10 January 2024, Prime Minister Rishi Sunak announced legislation to quash convictions en masse and speed up compensation for close to 980 affected workers, a step the government had not taken in the nearly five years since the High Court judgment. Days later, former Post Office chief executive Paula Vennells announced she was returning her CBE, after a petition calling for it to be stripped passed one million signatures.

The Bill, So Far

The Post Office (Horizon System) Offences Act 2024 quashed convictions by statute rather than requiring each case to go through the Court of Appeal individually. As of February 2025, 589 people had been identified as having at least one conviction quashed under the Act. Sir Wyn Williams' statutory inquiry published the first volume of its final report on 8 July 2025, setting out the scale of harm and recommending reforms to the compensation schemes.

As of 19 December 2025, roughly £1.38 billion had been paid out to more than 10,600 claimants across the various redress schemes, according to government data. Fujitsu, meanwhile, continued to hold UK government contracts throughout the years the scandal was being litigated and investigated, including contracts worth some £430 million awarded in 2022 — after the 2019 High Court judgment against Horizon, and while the public inquiry into its own software was already under way.

Sir Wyn Williams' inquiry could not say for certain how many sub-postmasters died before any compensation reached them, only that the number was substantial and that some cases were closed by their claimants' deaths rather than their vindication. Fujitsu built the software, the Post Office prosecuted the people it convicted of failing to account for what that software said was missing, and both organisations kept operating, and in Fujitsu's case kept winning government work, for years after each had been told, in writing, that the numbers could not be trusted.

Filed from public reporting:

• Al Jazeera — The Great British Post Office scandal explained
• Computer Weekly — Post Office Horizon scandal explained: Everything you need to know
• National Archives Caselaw — Bates & Others v Post Office Ltd, EWHC 2019
• Courts and Tribunals Judiciary — Bates v Post Office judgment (PDF)
• GOV.UK — Post Office Horizon financial redress data as of 19 December 2025
• Post Office Horizon IT Inquiry — Reports and statements
• Bloomberg — Fujitsu's Patterson Says It Knew About Post Office Horizon Bugs From the Start
• ITV — Mr Bates vs the Post Office is 2024's most watched programme
• Bloomberg — Rishi Sunak Announces Steps to Exonerate UK Post Office Scandal Victims
• NBC News — At least 13 may have killed themselves over UK's Post Office wrongful convictions scandal
• BBC News — Post Office false theft claim left me bankrupt
• The Register — Post Office boss Paula Vennells returns CBE