The government expects to report on the impact of pre-Horizon software system errors on subpostmasters by spring next year.
It said it is currently looking for an investigation firm to carry out the work, announced earlier this week, which will look at the wider impact multiple software systems had on subpostmasters’ businesses and lives.
“We are yet to finalise the scope of the investigation as a supplier has not yet been selected. We will be looking at a range of software and systems in place that pre-date Horizon,” said the government.
The Criminal Cases Review Commission (CCRC) has already stated that it is looking into multiple Post Office software systems that are potentially implicated in the miscarriages of justice suffered by subpostmasters.
Now, through the new investigation, the government plans to get a “fuller understanding” of these systems and “their impact” on subpostmasters.
The Post Office scandal was triggered by, but not caused by, software errors. It was the result of the Post Office’s policy of making subpostmasters pay for unexplained shortfalls that appeared on branch accounting systems. This policy did not just exist for Horizon but had in fact existed for many years and applied to unexplained shortfalls on any system used by subpostmasters.
The CCRC told MPs in January that there are 35 applications of interest, which it refers to as “pre-Horizon”. It said that any of these systems could be linked to miscarriages of justice, and it is not a giant leap to suggest that pre-Horizon software also caused unexplained shortfalls that subpostmasters were forced to cover.
Pre-Horizon systems of note include Capture, ECCO+, Automated Payment Service (APS)/Automated Payment Technology (APT) and ALPS/OBCS.
Read more about ECCO+: Post Office acknowledges ECCO+ user’s calls for help three decades ago.
Although the Capture system was used before Horizon, an investigation has already established its flaws, therefore it will not be included in the latest investigation, the government told Computer Weekly.
The establishment of Capture’s errors in an investigation by Kroll in 2024 ultimately contributed to the establishment of a compensation scheme, separate to those related to Horizon, for former Capture users. The CCRC began reviewing convictions based on data from the software and has so far referred two convictions based on Capture data to the Court of Appeal, with more being reviewed.
A conviction based on the APT/APS system was also referred to the Court of Appeal in December 2025. The 2001 conviction of former subpostmaster Gareth Snow was passed to the appeal court after the CCRC established that there was evidence that the APS/APT, which Snow used in his branch in Denbighshire, “could cause accounting errors”.
But the current cases and systems being reviewed “may represent just the tip of another iceberg”, said a select committee report in March. During the 1980s and 1990s, multiple systems were used in Post Offices to automate work before the introduction of the Horizon system. These early systems were susceptible to errors that users and the Post Office did not understand. In the same way as with Horizon, subpostmasters were contractually obliged to take responsibility for unexplained losses.
The CCRC has identified what it describes as 35 “pre-Horizon applications”.
The government said: “Consistent with our approach to the Capture software, an independent investigator will establish a fuller understanding of those software applications and their impact, providing government with a robust evidence base to inform any future considerations.”
The Post Office scandal was first exposed by Computer Weekly in 2009, revealing the stories of seven subpostmasters and the problems they suffered due to Horizon accounting software, which led to the most widespread miscarriage of justice in British history (see below timeline of Computer Weekly articles about the scandal since 2009).
