MP calls for review of computer evidence rule which led to subpostmasters being wrongly convicted

Labour MP Darren Jones has asked the minister in charge of the courts to look into the appropriateness of the rule on the use of computer evidence in court, in light of miscarriages of justice in the Post Office IT scandal.

He wrote to Lord Chancellor Alex Chalk urging him to consider the issue personally after the government earlier disagreed that the rules should be changed.

Jones is the chair of the House of Commons Business and Trade Select Committee, which has been investigating the Post Office and its behaviour in regard to the Horizon IT scandal.

In 2009, a Computer Weekly investigation revealed that subpostmasters were being blamed for unexplained accounting shortfalls, which they believed to be caused by software errors (see all Computer Weekly articles on the scandal below).

Many of these subpostmasters were sent to prison, and those prosecuted suffered huge financial difficulties and stress, with many suffering bankruptcy. As the Post Office scandal was exposed, it emerged that the evidence from the Post Office’s Horizon computer system, used in thousands of branches, was error-prone, with figures that should not have been relied on in court.

A High Court group litigation order in 2018/19 saw a group of subpostmasters prove that computer errors caused unexplained accounting shortfalls. A total of 86 former subpostmasters have so far had criminal convictions overturned, and more are expected. It is today seen as one of the biggest miscarriages of justice in British history, one that was made possible because of a change to the rules around computer evidence brought in at the same time the Horizon system was rolled out to thousands of Post Office branches.

In 1999, at the same time the Horizon computer system automated manual accounting processes in branches, a presumption was introduced into law on how courts should consider electronic evidence. 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. This legal presumption replaced a section of the PACE Act 1984, which stated that those introducing computer evidence should be able to prove that it was in fact operating properly.

The new rule 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. As Computer Weekly revealed in 2021, following a response to a freedom of information (FoI) request made by computer scientist Steven Murdoch at University College London, the Post Office wrote to the Law Commission in 1995 when the law change was being proposed. It said 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.

Jones wrote: “The law, in short, says that the computer evidence must be deemed true unless a defendant can prove otherwise.” He added that “this is clearly out of date and needs review”.

He questioned whether the Criminal Procedure Rules Committee has the necessary resources to “proactively consider the issue”, adding: “I ask you to personally look at the issue, not least given the much wider implications today, to accelerate an appropriate review.”

In May last year, Kevan Jones, Labour MP and long-time campaigner for justice for the subpostmasters affected by the Horizon scandal, asked the secretary of state for justice whether the government planned to assess the legal presumption of reliability of computer evidence.

In response, Conservative MP and Parliamentary under-secretary of state for justice, James Cartlidge, said: “We have no plans to review the presumption, as it has wide application and is rebuttable if there is evidence to the contrary.”

He said the current public inquiry into the Post Office Horizon scandal would advise the government on the matter.

The government has said the Ministry of Justice will work with the Criminal Procedures Rules Committee to ensure lessons are learnt from the public inquiry in relation to the use of computer evidence.

There is a significant body of opinion, in IT and legal circles, that agrees that change to the guidance on the use of computer evidence in court must be made to avoid miscarriages of justice such as those experienced by subpostmasters.

Barrister Paul Marshall and others, who represented subpostmasters who successfully overturned wrongful convictions by the Post Office, was invited in August 2020 by MP Alex Chalk at the Ministry of Justice to submit a paper to the department on suggestions for improving the existing approach to the proof in court proceedings of computer-derived evidence. The paper was submitted to the MoJ and published. 

It recommended that when electronic evidence is used in legal proceedings, the party relying on the electronic evidence should automatically provide sufficient details of their systems to demonstrate that they are professionally managed.

Marshall told Computer Weekly that “it is difficult to imagine a more wrong-headed set of propositions” than those used to support and justify the change to law on computer evidence that was introduced in 1999. He said the judgements of High Court judge Peter Fraser in the 2019 group litigation action, where subpostmasters proved that computer errors were to blame for unexplained losses, exposed “the fundamental flaws in the Law Commission’s analysis and in its conclusions. It also exposes, tragically, how strikingly unfairly the presumption that a computer is working properly may operate in legal proceedings.”

“No computer scientist or expert would support or endorse the position in English law because it is simply wrong.”

He said that since the change to the rules, it has been assumed as a matter of law “that the computer worked properly unless it can be shown that that assumption cannot safely apply”, and that this puts an evidential burden on someone, responding to computer evidence, that in many cases they are simply incapable of doing, “for the simple reason they do not – and cannot – know”.

“The Horizon scandal in large part is the consequence of the Law Commission’s misconceived recommendations to parliament that PACE 1984 should be repealed,” said Marshall.

“The timeline of Post Office prosecutions matches exactly the period from which it was repealed. The Post Office had supported repeal – presumably to make its prosecutions for alleged ‘shortfalls’ easier and reversing the burden of proof was of immense practical value to the Post Office.”