Change to rules on computer evidence will be an ‘outcome’ of Post Office scandal

The Post Office’s head of investigations told public inquiry that, as a result of the Post Office scandal, court rules on computer evidence could go back to not presuming a system worked properly.

Giving evidence in a recent hearing at the statutory public inquiry examining the scandal, John Bartlett, director of assurance and complex investigations at the Post Office, said that he expects a return to rules that were in place before the change in 1999.

In 1999, a presumption was introduced into law on how courts should consider electronic evidence. This changed was used by the Post Office and caused one of the biggest miscarriages of justice in British history.

The rule followed a Law Commission recommendation for courts to presume that a computer system has operated correctly unless there is explicit evidence to the contrary. The legal presumption replaced a section of the PACE Act 1984, which stated that computer evidence should be subject to proof that it was in fact operating properly.

This made it easier for the Post Office, through its private prosecution powers, to convict subpostmasters for financial crimes when there were accounting shortfalls based on data from the Horizon system. Hundreds of subpostmasters were wrongly convicted of crimes such as theft and false accounting when they experienced unexplained losses. Prosecutions were based on a presumption that the software used in branches, known as Horizon, was working.

When the Horizon system showed unexplained shortfalls, after its introduction in 1999, subpostmasters were often prosecuted by the Post Office. Due to the change in legal rules on the use of computer evidence, courts would presume the system was working. But this was proved to not be the case during a High Court group litigation order in 2018/19. During the court trials, 555 subpostmasters proved the system was not robust and could create unexplained shortfalls.

Since the airing of a dramatisation of the Post Office Horizon scandal on ITV, hundreds of former subpostmasters have had convictions overturned or are waiting for them to be quashed.

Academics, lawyers and tech experts have been campaigning for years to change this rule and the Post Office scandal has brought the issue to the fore.

During a recent public inquiry hearing, Bartlett, a former police officer, said: “I think one of the outcomes of the scandal is that, for all cases, irrespective of whether they’re Post Office derived, linked or otherwise, law enforcement are going to have to do those verification exercises, assurance exercises, on digital data, because I think the scandal has shown that the assumption made that systems could be relied upon has changed.

“I remember when I first joined the police, there was no natural assumption that a computer system was functioning and workable, and we had to do what were called system statements. I think an outcome of the scandal is that law enforcement will end up going back [to that]. So, I don’t think it will be particular to us.”

The Post Office emphatically supported the change in the rules introduced in 1999. Computer Weekly revealed in 2021, following a response to a freedom of information request made by computer scientist Steven Murdoch at University College London, that the Post Office wrote to the Law Commission in 1995 when the law change was being proposed. It wrote that the rule at the time, which said computer evidence should be subject to proof that it was in fact operating properly at the time, was “somewhat onerous” when prosecuting people charged with crimes, such as the subpostmasters that run and own its branches.

In response to a Law Commission request for feedback on proposals to change the rules, the Post Office wrote: “I consider that computer evidence is, in principal, no different from any other sort of evidence, and it should, in general terms, be admissible, so that any argument in court would be related to its weight rather than its admissibility.

“I therefore consider that there should be a presumption that the machine is in working order, etc, and if the defence wish to argue otherwise, then clearly, they should be able to do so. At present, I therefore consider the evidential requirements to be far too strict and can hamper prosecutions.”

It continued: “In the event of a subpostmaster being prosecuted for theft or false accounting, the Post Office may need to rely upon the computerised accounting records. The subpostmaster is frequently the only person who can give the evidence required by Section 69 of [PACE]. In the absence of admissions or other direct evidence, the Post Office may not be able to prove the case solely on the ground of being unable to satisfy the technical requirements of Section 69 of [PACE].”

The Post Office was making clear that prosecutions would be difficult unless the computer evidence is presumed to be accurate. What is common knowledge today is that the Horizon software, which Post Office branches used, produced figures that were not accurate at all times. This data was used to successfully prosecute hundreds of people, which are now being overturned, in what is often referred to as the widest miscarriage of justice in history.

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).

• Also read: What you need to know about the Horizon scandal •

• Also watch: ITV’s documentary – Mr Bates vs The Post Office: The real story •

• Also read: Post Office and Fujitsu malevolence and incompetence means huge taxpayers’ bill •