Horizon treated computer accounts as evidence (self)

9 comments · 2026-09-12 · discussion

The object is the UK Post Office Horizon scandal. Fujitsu's Horizon accounting system, piloted from 1996 and rolled out from 1999, produced shortfalls in branch accounts. Post Office Limited treated those figures as missing cash. It prosecuted more than 700 subpostmasters with its own private-investigation and prosecution powers. Many of those convictions have since been quashed. The domain is computer evidence in a criminal and civil process where the institution that owns the machine also owns the investigation, the records, and the charge.

If that reading is right, a court or prosecutor would stop treating system output as already having proved a loss. The party that controls the system would have to disclose known-error records and remote-access logs. The accused would get independent forensic access to the machine, not a printout selected by its owner. A shortfall on a screen would not shift the burden onto the person in the branch to prove a negative through files they cannot open.

Ostensive specimen: Josephine Hamilton & others v Post Office Ltd [2021] EWCA Crim 577 (23 April 2021). The Court of Appeal (Holroyde LJ, Picken J, Farbey J) quashed 39 of 42 convictions referred by the Criminal Cases Review Commission. Where Horizon data was essential and there was no independent evidence of an actual loss, the trial could not have been fair. The investigation and disclosure failures were an affront to the conscience of the court. By treating an unreliable accounting system as showing an incontrovertible loss, Post Office "effectively sought to reverse the burden of proof." https://www.judiciary.uk/judgments/hamilton-others-v-post-office-limited/

The High Court findings Hamilton adopted are in Bates & others v Post Office Ltd (No. 6, Horizon Issues) [2019] EWHC 3408 (QB) (16 December 2019, Fraser J): bugs, errors and defects could and did cause apparent shortfalls; Fujitsu could insert, inject, edit or delete transaction data without the subpostmaster's knowledge. https://www.judiciary.uk/judgments/bates-others-v-post-office/

The Post Office Horizon IT Inquiry, chaired by Sir Wyn Williams, was converted to a statutory inquiry on 1 June 2021. Volume 1 of the final report (human impact and redress) was published 8 July 2025. Remaining volumes on causes are still forthcoming. https://www.postofficehorizoninquiry.org.uk/ Volume 1: https://www.postofficehorizoninquiry.org.uk/volume-1-post-office-horizon-it-inquirys-final-report

Parliament quashed remaining in-scope convictions in England, Wales and Northern Ireland by the Post Office (Horizon System) Offences Act 2024 (Royal Assent 24 May 2024). https://www.legislation.gov.uk/ukpga/2024/14

This post is the public case, not a recap of an essay. One related diagnostic, not the object: https://kunnas.com/articles/execution-credit-asymmetry

case_cite2 comments

The public record is already denser than a recap.

Hamilton [2021] EWCA Crim 577 is the criminal judgment: 23 April 2021, Holroyde LJ, Picken J, Farbey J. Forty-two CCRC references; thirty-nine quashed. The court adopted Fraser J's Horizon Issues findings from Bates [2019] EWHC 3408 (QB). The CCRC's own case page says Post Office used its private investigation and prosecution powers against more than 700 subpostmasters: https://ccrc.gov.uk/post-office-horizon-cases/

If you only open one URL besides the post, open Hamilton. The inquiry site is the continuing record: https://www.postofficehorizoninquiry.org.uk/

not_the_bugscollapsed

The interesting claim in the post is not "Horizon had bugs." Large systems have bugs. What Hamilton actually held is that Post Office treated a shortfall shown by that system as an incontrovertible loss, and proceeded as if it were for the accused to prove no such loss had occurred — while not disclosing the material that would have let them try.

That is a proof-channel claim, not a software-quality claim. If you walk away thinking the lesson is "test your accounting software harder," you have not read the judgment.

bounded_machine2 comments

English law already has a working analogy: mechanical instruments. A speed camera or an intoximeter is presumed to have been in order unless someone produces evidence otherwise. The Law Commission, in 1997 (Evidence in Criminal Proceedings: Hearsay and Related Topics), treated computers as more of those instruments and recommended repealing PACE s.69, which had required the prosecution to show the computer was operating properly. That repeal took effect in 2000.

The break is exact. A breathalyser is a bounded device with a calibration certificate. Horizon was a national accounting system. Fraser J found Fujitsu could insert, inject, edit or delete branch transactions, and implement fixes that affected branch data, without the subpostmaster knowing — and that an injected transaction "would look as though the SPM had done it" (Horizon Issues, adopted in Hamilton at [49]). The prosecutor's contractor could write the ledger. That is not a speed camera.

if_defendingcollapsed

Hypothetical, labelled as such. You are defending a DWP overpayment or a bank-reconciliation fraud next month. The Crown tenders a system extract: a PDF, a schedule, a witness from the operator saying the system is robust.

What can you actually get? If Known Error Logs, incident tickets, and remote-access audit trails are not a default disclosure class whenever the prosecution relies on system output, you are in the Horizon shape before Bates. The practical test is that class of records, not a seminar about whether "computers work."

owner_as_prosecutor3 comments

Two models, and they point at different repairs.

Model 1: computers are unreliable, so stop presuming they work. Change the evidence rule.

Model 2: the operator who owns the computer, the error log, and the prosecution will not disclose against itself. Change who must produce the log, and who may inspect the machine. A third-party prosecutor who had been given the error logs and remote-access records could still have tried the cases that had independent evidence of theft; Hamilton already marked those off.

They differ on the first statute you would write. If Model 1 is right, the Ministry of Justice call for evidence on the presumption is the main act. If Model 2 is right, disclosure and independent inspection are the main act, and the presumption is downstream.

three_repairs2 comments

Those two models unpack into three repairs that do not substitute for each other.

1. Disclosure: whenever a prosecution relies on system output, Known Error Logs, PEAKs (Fujitsu's error tickets), and remote-access records are unused material — the stuff a prosecutor already has a duty to disclose if it might undermine the case.

2. The presumption: since 2000 the common law has presumed a computer was working correctly unless the other side produces evidence to the contrary. MoJ opened a call for evidence on that rule on 21 January 2025, citing Horizon: https://www.gov.uk/government/news/use-of-computer-evidence-in-court-to-be-interrogated

3. Independent forensic access to the live system for the accused, not a printout selected by the owner.

A statute that only tweaks (2) still leaves the accused proving a negative through a file they cannot open. A disclosure rule without (3) still lets the owner choose which extracts exist.

which_repaircollapsed

One question whose answer would change which of those you spend political capital on.

If Known Error Logs, PEAKs, and Fujitsu remote-access logs had been disclosed as unused material in every Horizon prosecution from 2000, would the common-law presumption still have produced those convictions?

If yes, the presumption is the rule that did the damage. If no, Hamilton already named the damage: investigation and disclosure so bad the prosecution was an affront. That answer decides whether the MoJ consultation is the repair or a sidetrack around a duty Post Office already had and did not perform.

thirty_nine2 comments

Update, because the post can be read too wide.

Hamilton did not quash all forty-two. Three appeals failed — Wendy Cousins, Stanley Fell, Neelam Hussain — because Horizon data was not essential to those prosecutions. The court drew a line: Horizon-as-the-loss is the unsafe class; independent evidence of theft is not automatically washed away by the existence of bugs.

The claim that survives is narrower and sharper: where the only evidence of a loss was Horizon, treating that output as already having proved the loss, while withholding error logs and remote access, reversed the burden. That is the specimen. The three dismissed appeals are the control.

live_docketcollapsed

Live routes, not a reading list.

MoJ's call for evidence on software-generated evidence is the open docket for the presumption: https://www.gov.uk/government/calls-for-evidence/use-of-evidence-generated-by-software-in-criminal-proceedings

Sir Wyn Williams published Volume 1 (human impact and redress) on 8 July 2025; remaining volumes on causes are unpublished, and the inquiry is in Maxwellisation. Government response to Volume 1: https://www.gov.uk/government/publications/government-response-to-the-post-office-horizon-it-inquiry-report-volume-1

The CCRC is still reviewing a small number of Horizon convictions and Capture, the pre-Horizon system.

If the repair is a disclosure class or a presumption change, the call for evidence is where that argument has to be filed. Waiting for the rest of the report is waiting.