Post Office branch accounts showed apparent shortfalls that led to prosecutions and devastating consequences for subpostmasters. The 2019 Horizon Issues judgment examined bugs, errors and defects, rather than accepting the system as infallible. In 2021, the Court of Appeal quashed 39 convictions as unsafe.
A computer-generated figure can look neutral while depending on imperfect software, incomplete investigations and undisclosed technical knowledge. The litigation forced those components apart. The question was not whether a screen displayed a shortfall, but whether the shortfall reliably established money had been lost or stolen.
The scandal is a warning about institutional confidence becoming evidence in its own favour. Challenges could be treated as failures of the individual instead of prompts to investigate the system. The judgments provide the strongest starting point: they describe what was tested and found, rather than leaving the story at a slogan about bad computers.
The established record.
- 01
The High Court examined Horizon’s reliability in 2019.
- 02
Bugs, errors and defects could cause apparent branch discrepancies.
- 03
The Court of Appeal quashed 39 convictions on 23 April 2021.
How the story unfolded.
- 1999 onwards
Horizon enters branch accounting
Apparent discrepancies lead to disputes and prosecutions.
- December 2019
Technical confidence is tested in court
The Horizon Issues judgment examines defects and reliability.
- 23 April 2021
Convictions are quashed
The Court of Appeal allows 39 appeals.
Where the evidence stops.
These judgments concern specific litigation and appeals. They do not automatically determine every individual case or establish that every discrepancy had the same technical cause. The wider inquiry and compensation questions have their own records.
Read the original sources.
The source may establish a narrower point than the headline. Follow the specific finding, its date and its limitations.
What evidence should be required before a machine-generated accusation becomes a criminal one?