More than 900 subpostmaster convictions wouldn’t have happened without Post Office-backed law change

The IT expert who represented Alan Bates and more than 500 subpostmasters in a High Court case against the Post Office said if changes to the rules on computer evidence, described as “onerous” by the Post Office, had not been made in 1999, about 900 subpostmaster convictions wouldn’t have happened.

In May 2022, the government said it had no plans to review the current law, described as “wrongheaded” by one lawyer, but the recent outpouring of public anger, which has already caused the government to introduce constitutionally unprecedented emergency legislation to overturn 800 convictions en masse, could make this the time to review the rules.

Expert IT witness Jason Coyne told Computer Weekly that none of those 900 or so convictions would have happened had the law on computer data used in court not been presumed to be accurate. Coyne represented Bates and others in High Court Group Litigation Order (GLO), where the 555 former subpostmasters proved that the Horizon computer system used in branches up and down the country was causing account shortfalls, which they were blamed and punished for. Around 900 were convicted of crimes such as theft and false accounting as a result.

Following the overturning of 95 convictions since the High Court case and a public backlash from an ITV drama revealing the devastation the Post Office inflicted on subpostmasters, the government has announced its emergency legislation to quash the convictions of around 800 former subpostmasters. With proof that the government can react so quickly, exonerating people convicted based on computer evidence, experts call for a change of the rules around the use of computer evidence that led to the wrongful conviction in the first place.

In 1999, coincidentally the year Horizon was rolled out to thousands of branches, the rule on the use of computer evidence was changed from demanding the prosecution prove the computer worked properly, to placing the responsibility on the defence.

The Post Office supported a proposal in 1995 to change Section 69 of the 1984 Police and Criminal Evidence Act (PACE), which, at the time, stated that computer-based evidence should be subject to proof that the computer system was operating properly. It said the rule was “somewhat onerous” when prosecuting people charged with crimes, such as the subpostmasters who run and own its branches.

Coyne said: “If it were not for the presumption that computer evidence is correct unless it can be proven otherwise, none of these would have gone through, because they would have had to have shown that the system didn’t suffer from any faults that could have impacted branch accounts, and there is not a chance that they could have ever done that.”

For the 2018 High Court GLO, Coyne created a table of software flaws which revealed bugs, errors and defects that “pretty much covered the entirety of the operation of Horizon”, he said.

Reform of the law is the right route, according to Coyne. “It can’t be the case that we just simply look at a computer system and say, ‘If that is what the computer system says, it is reliable’, without investigating all the surrounding circumstances which might have had an impact on that particular piece of data. We have to be able to test that data and prove that it is robust or certainly that it is robust beyond any reasonable doubt.”

He has first-hand experience of the Post Office failing to prosecute when computer evidence was challenged. In 2003, Coyne was appointed as a joint expert witness for both the Post Office and defendant Julie Wolstenholme, who was subpostmaster at the Post Office Branch in Cleveleys, Lancashire.

Coyne was only given access to logs of helpdesk calls made by Wolstenholme to attempt to ascertain if computer errors were causing her problems, because audit data had been destroyed due to the time that had lapsed.

In his report, Coyne said 63 of the calls were “without doubt” related to system failures, either hardware, software or interfaces, and only 13 of the calls he looked at “could or should” have been considered as Wolstenholme requesting help or guidance.

The Post Office, which Coyne described as “delusional”, tried, unsuccessfully, to convince him that he was wrong when his report put its case against a subpostmaster in doubt, and it ended the action, settling with the defendant when he refused to change his view.

Computer Weekly knows of other cases when the Post Office dropped charges after subpostmasters challenged the computer system with experts involved.

Computer Weekly first exposed the scandal in 2009, with the stories of seven subpostmasters and the problems they suffered as a result of the Horizon system (see timeline of all Computer Weekly articles below).