UK Post Office used faulty accounting software to wrongly accuse over 900 subpostmasters of theft and fraud
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Occurred: 2009-
Page published: October 2022 | Page last updated: December 2024
The UK Post Office used faulty accounting software to wrongly accuse over 900 subpostmasters of theft and fraud, leading to hundreds of wrongful convictions, bankruptcies, and severe personal tragedies, caused by a systemic failure to prioritise human lives over the perceived infallibility of a technology system.
What happened
What happened
Between 1999 and 2015, the UK Post Office prosecuted hundreds of subpostmasters (and many others via the Crowm Prosecution Service) based on financial discrepancies apparently reported by the Horizon IT system.
The actual harm was devastating: hundreds of innocent people were imprisoned, thousands lost their livelihoods and life savings, many were shunned by their communities, and the stress led to broken families, ill health, and at least four confirmed suicides.
Even those not prosecuted were often forced to "repay" non-existent shortfalls out of their own pockets.
Why it happened
Why it happened
The cause of the scandal was a catastrophic failure of socio-technical governance. The Post Office and the developer, Fujitsu, treated the software’s outputs as "gospel" despite knowing as early as 1999 that the system contained significant bugs and defects.
The Post Office repeatedly told individual subpostmasters they were "the only ones" having issues, despite widespread systemic errors.
Legal "presumption" at the time assumed computer systems were operating correctly unless proven otherwise, placing an impossible burden of proof on individuals who had no access to the underlying code or error logs.
Internal Post Office incentives rewarded "defending the system" and protecting the Post Office brand at all costs over investigating the truth.
What it means
What it means
For subpostmasters and their families, the scandal resulted in wrongful imprisonment, loss of earnings and livelihoods, debt, bankruptcies, trauma and suicides.
For society, it serves as a "canonical failure," highlighting the dangers of "black box" public sector automation. It also raises serious questions about the accountability of the individuals and organisations designing, developing and managing the Horizon System.
System 🤖
System 🤖
Horizon
Operator: Post Office
Developer: Fujitsu/ICL
Country: UK
Sector: Govt - retail
Purpose: Make benefits payments; Reduce fraud
Technology: Automated accounting system
Issue: Accountability; Accuracy/reliability; Automation bias; Employment/labour; Transparency
Transparency, accountability 🙈
Transparency, accountability 🙈
The Post Office Horizon system has been widely criticised for its lack of transparency and accountability, including:
Audit trails. The system did not provide clear audit trails, making it difficult to track changes to financial data and identify errors or discrepancies.
Transaction data. The system did not provide sufficient access to or visibility of transaction data, making it difficult for subpostmasters to identify and investigate discrepancies.
System bugs and fixes. The Post Office did not provide clear information about system bugs and fixes, making it difficult for subpostmasters to understand the root cause of errors.
Complaints and appeals processes. There was no clear process for reporting errors or discrepancies, and subpostmasters were often discouraged from reporting issues.
Independent oversight. The system was not subject to independent oversight, and the Post Office had significant control over the system and its data.
Legal opacity. The long-running Post Office scancal involved the obfuscation, blocking and delayal of mediation and litigation procedures, amongst other legal and reputational defensive tactics.
Timeline ⏰
Timeline ⏰
1996–1999: Pilot and national rollout of the Horizon system.
2000–2015: Peak period of wrongful prosecutions and internal "shortfall" collections.
2009: Computer Weekly publishes the first major exposé; the Justice for Subpostmasters Alliance (JFSA) is formed.
December 2019: UK High Court "Bates v Post Office" ruling confirms Horizon was not "remotely robust"', contained 'bugs, errors and defects', and constituted a 'material risk' that shortfalls in branch accounts were caused by the system. The ruling saw the Post Office agreeing to settle with 555 claimants, having accepted that it had previously 'got things wrong in [its] dealings with a number of postmasters'. It was to pay GBP 58m in damages.
February 2020. The UK government announces it will would hold an official independent inquiry into the scandal.
June 2021: Court of Appeal begins quashing convictions en masse; a Statutory Public Inquiry is launched.
September 2023. The UK government offers Post Office workers with wrongful convictions for theft and false accounting GBP 600,000 each in compensation.
January 2024. The UK government says it will introduce legislation to exonerate wrongfully convicted.
2024: National outcry following the TV drama Mr Bates vs The Post Office leads to the Post Office (Horizon System) Offences Act 2024, quashing hundreds of convictions.
January 2026: The main Horizon Shortfall Scheme (HSS) closes to new applications amid concerns that many eligible victims have yet to come forward.
Legal, regulatory 👩🏼⚖️
Legal, regulatory 👩🏼⚖️
Investigations, assessments, audits 👁️
Investigations, assessments, audits 👁️
AIAAIC Respository ID: AIAAIC028
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