UK Post Office’s Horizon IT system flaws drove users to consider suicide, inquiry finds

Post Office managers and supplier Fujitsu allowed erroneous data from the Horizon IT accounting system to be used to prosecute hundreds of innocent sub-postmasters, despite knowing it was flawed, the first part of a report on the UK’s biggest ever IT scandal has found.  

The results of this mismanagement were devastating, with the report estimating that prosecutions by the Post Office were a factor in at least 13 suicides, with a further 59 people telling the Horizon IT inquiry that they contemplated taking their own lives.

As one sub-postmaster testified: “The mental stress was so great for me that I had a mental breakdown and turned to alcohol as I sunk further into depression. I attempted suicide on several occasions and was admitted to a mental health institution twice.”

What has yet to be determined — and could yet result in criminal prosecution — is why managers persisted with prosecutions for alleged fraud over so many years, despite ample evidence that Horizon was prone to serious errors.

Hundreds of prosecutions

Horizon was launched in 1999 by Fujitsu, which had acquired it as part of its takeover of ICL the previous year. Designed to automate sales, stocktaking, and accounting across 18,500 post offices, the system was deployed in two phases: what is now called ‘legacy’ Horizon between 1999 and 2010, and Horizon Online, or HNG-X, after that.

Horizon’s role was to modernize a paper accounting system with one that recorded all money going into and out of sub-postmasters’ accounts using a centralized online database.  

However, even before launch, Fujitsu was aware that Horizon was prone to intermittent “bugs, errors and defects,” the report found. But despite Post Office managers knowing this, “throughout the lifetime of Legacy Horizon, the Post Office maintained the fiction that its data was always accurate,” the report said.

The hundreds of prosecutions that resulted from this are now viewed as the largest miscarriage of justice in British history. It discredited not only the Post Office and Fujitsu managers, but the criminal justice system that for years remained blind to ongoing miscarriages despite repeated complaints by campaigners.

“All of these [prosecuted] people are properly to be regarded as victims of wholly unacceptable behavior perpetrated by a number of individuals employed by and/or associated with the Post Office and Fujitsu from time to time, and by the Post Office and Fujitsu as institutions,” said the report.

Infallibility fallacy

Horizon’s Achilles’ heel was its tendency to generate apparent accounting shortfalls in the sub-postmaster accounts, in some cases for large sums.

The contract between the Post Office and the self-employed sub-postmasters made the latter liable for these losses. When a shortfall was flagged, sub-postmasters were asked to pay the money back, or, in more than 900 cases, were prosecuted for theft.

In 17 prosecutions the Horizon IT Inquiry Report examined in detail, the choice was stark – financial ruin, or jail time for the accused, and in some cases, both.

The underlying weaknesses of Horizon have already been well documented, including by technology journalists who were instrumental in exposing the system’s shortcomings as early as 2010. These included bugs that could cause the system to create multiple phantom withdrawals, to double payments, or to generate old-fashioned rounding errors.

The obvious conclusion is that the system was poorly coded, with not enough testing and revision to iron out flaws. Feedback from sub-postmasters was routinely ignored, with managers sticking to the belief that the system could not be wrong.

One might speculate that this was partly a feature of the 1990’s mindset from which Horizon emerged. Centralized databases and accounting systems were seen as the future, and too many assumptions were made about their infallibility.

The report has yet to make a judgment on why the system was trusted for so long, and it’s possible that managers at first believed Horizon was uncovering genuine fraud.

At some point, however, this stopped being the case, the report said. The implication is that managers at Fujitsu and the Post Office knew that Horizon was generating imaginary shortfalls and decided to cover that up to protect themselves and their institutions.

This week’s findings are part one of the inquiry, and focus primarily on the human effects of the Horizon IT scandal. A second report is expected later in 2025 or in 2026 which will examine the specific flaws in the Horizon’s system in more detail. It will also assess any wrongdoing by managers.

For the wider IT sector, the effects of the Horizon IT scandal could continue to linger. Large IT projects from the 1990s already have a poor reputation in the UK, with several going over budget or failing to deliver their expected returns. Horizon – now a watchword for incompetence and moral failure – has only amplified this widely held view.No more blue screens: How Microsoft is making Windows more resilient – ComputerworldRead More