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Post Office scandal: The rise of computers and the decline of English justice

The Post Office prosecuted its subpostmasters up and down the country with a zeal that would not have embarrassed the Inquisition

If the administration of criminal justice in England and Wales was an airline, no one would fly it, such is the level of failure – but it’s the only show in town. 

Few really care, or think that a wrongful conviction could happen to them. Unfortunately, hundreds of subpostmasters, many of whom went to prison, thought just that.

Around 700 subpostmasters and Post Office branch employees are expected to be shown to be victims of this miscarriage of justice. Some have died. Recently, 47 had their convictions quashed by the Court of Appeal and by Southwark Crown Court, the Post Office having been found to have seriously abused the processes of the court over a period of about 13 years. 

How can this have been allowed to happen?

The wearing of 18th-century wigs – and dressing gowns – does not help, resonating, as these do, with a bygone age before bits, bytes and bugs – at least electronic. (Don’t even think about deep learning neural networks and artificial intelligence.)

In 1997, Lord Hoffmann, widely acknowledged as a clever judge, expressed his opinion that “[i]t is notorious that one needs no expertise in electronics to be able to know whether a computer is working properly”. In his book, On the psychology of military incompetence, psychologist Norman Dixon called this “pontification” – a tendency of those in high office to make statements on issues of which they know little. 

Flawed system palmed off to post offices

As though prompted by Hoffmann’s sage-like insight, in 1997 and 1999, the Law Commission recommended that Parliament should amend the civil and criminal law so that computers should be treated like machines and be considered to be “working properly” absent evidence to the contrary.

In doing so, the Law Commission expressed its view that computer errors are readily detectable to an operator and are often the result of input errors. Previously, it was necessary for a person relying in court proceedings upon evidence from a computer to prove that it was working properly at the relevant time. Expert assistance might have pointed out that computers are not machines, or at least not simply machines, and that coding error rates in commercial software are typically around 30 per thousand lines of code (significantly less for safety-critical software).

“Nothing short of a public inquiry will explain this catastrophe or offer the prospect of restoring public confidence. It surprises me that the government cannot see this”

Paul Marshall, barrister

Parliament’s acceptance of the commission’s recommendation was good news for the Post Office. In 1999, it agreed to take on the disastrous UK government Horizon computer system project that, by then, had wasted about £700m in taxpayers’ money. Government ministers had concluded that Horizon was insufficiently evaluated for the Benefits Agency, its intended use, and considered that it exposed the government to risk of a catastrophe, for which it had no appetite. 

With the assistance of its lawyers, the Post Office drafted a one-sided contract that shifted the commercial risk of bugs and systemic failure onto unsuspecting subpostmasters. If the computer system malfunctioned, it was for the unfortunate subpostmaster at the village post office to prove why – in practice, impossible.

As late as 2019 the Post Office questioned that a Horizon computer known errors log existed. When it was established that it did, the Post Office denied it was relevant. When it was established that it existed and was relevant, the Post Office complained it was not its log to disclose, because Horizon’s supplier, Fujitsu, had it. High court judge Sir Peter Fraser pointed out that the Post Office was contractually entitled to it. Game up, after 20 years.

In the meantime, the Post Office prosecuted its subpostmasters up and down the country with a zeal that would not have embarrassed the Inquisition. So-called “audits” (in truth merely cash balance checks) were conducted by the Post Office’s security department incentivised by the number of failed audits it achieved. 

Denied a fair trial

Subpostmasters were prosecuted and convicted with the gratifying ease of shooting fish in a barrel. At Seema Misra’s trial in October 2010, the prosecution (the Post Office as private prosecutor – but formally “the Crown”) taunted her before the jury for her inability to point to any failure or error in the working of her Post Office Horizon computer terminal. Prosecuting counsel told the jury that any problem with the computer system would be identifiable to a Post Office branch terminal operator. It was as though counsel had taken on board Lord Hoffmann’s comment and the Law Commission’s recommendations. 

Misra made four applications to three different judges asking for further disclosure from the Post Office. It responded by telling the judges that, should she point to what it was she wanted, it would be happy to oblige. Her defence counsel complained she could not have a fair trial without further disclosure. The trial judge considered that documents provided by the Post Office were quite sufficient for her trial to be fair.

Less than a month before Misra’s trial, the Post Office and Fujitsu had held a high-level meeting attended by senior representatives of both companies. They discussed a “Receipts and Payments” mismatch bug that could cause balancing errors that would be invisible to a Horizon branch terminal operator. It was minuted that this might affect “ongoing legal cases” and impact confidence in the Horizon system.

The expert witness for the Post Office who gave evidence against Misra at her trial, a senior electronic engineer employed by Fujitsu, was present at that meeting but said nothing. She was convicted of theft and sentenced to imprisonment. She was eight weeks pregnant and imprisoned on her son’s 10th birthday. 

On 16 December 2019, Judge Fraser, in a 1,482-paragraph judicial tour de force, laid bare by his judgment the fallacy of Lord Hoffmann’s statement and the fatal error in the Law Commission’s recommendations to Parliament. He described the Receipts and Payments mismatch bug as having been “kept secret” by the Post Office.

There are no votes in justice, let alone criminal justice. Between 2010 and 2019, investment in the justice system in England and Wales was cut by 24% in real terms. Imagine what the NHS would look like after such cuts.

Nothing short of a public inquiry will explain this catastrophe or offer the prospect of restoring public confidence. It surprises me that the government cannot see this.


Paul Marshall is a barrister who, before illness, practised commercial law. Marshall and his junior, Flora Page, offered their services free of charge to three former subpostmaster appellants: Tracy Felstead, Janet Skinner and Seema Misra. All three had their convictions overturned in the Court of Appeal on 23 April 2021.

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