Post Office scandal furore is moment to change digital evidence rules

With the general public now alert to and furious over the mistreatment of subpostmasters, the government must take the opportunity to change the law that made it easy for the Post Office to wrongly convict people based on computer evidence.

Following a hard-hitting drama and documentary on ITV, the Post Office Horizon scandal is now receiving the attention it deserves, sparking anger across the UK and a kick up the backside for a government that has failed subpostmasters.

With public opinion the only force that many politicians listen to, it is inevitable that there will be enough MPs to finally force action on the slow progress in compensating victims and address the hundreds of potentially wrongful convictions of subpostmasters.

The Post Office Horizon scandal saw hundreds of subpostmasters prosecuted based on computer evidence after they experienced unexplained shortfalls in their accounts. The IT system used by subpostmasters, known as Horizon, was later proved to be error-prone, casting doubt on prosecutions.

Over a 15-year period, more than 900 subpostmasters were prosecuted for financial crimes based on data from the Fujitsu Horizon software. Many claimed the data was wrong – and they were proved right years later in the High Court.

Computer Weekly exposed the scandal in 2009 with an investigation into problems being experienced by seven subpostmasters. Nearly 100 former subpostmasters have now had criminal convictions quashed, with many more expected in what is described as the widest miscarriage of justice in UK history.

While the government quite finally and quite rightly puts its focus on addressing problems in compensation and conviction appeals, there is another wrong that needs to be righted – the rules around the use of digital evidence. Not only did the Court of Appeal find the convictions to be wrongful, but labelled them “an affront to justice”.

In 1999, the government-owned Post Office began installing a new core accounting and retail system, known as Horizon, in thousands of Post Office branches across the country. The system, supplied by Fujitsu, was seen as a revolution at the time, automating manual tasks such as bookkeeping.

At around the same time, a presumption was introduced into law on how courts should consider electronic evidence. The new rule introduced in 1999 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 Police and Criminal Evidence Act (PACE) 1984, which stated that computer evidence should be subject to proof that it was operating properly.

Because the 1999 legal rule meant data from the Horizon system was presumed accurate, losses were considered the fault of the subpostmaster, whether through theft or incompetence. Subpostmasters were forced to use their own cash to cover shortfalls or, in many cases, were prosecuted for theft and false accounting if they couldn’t afford, or refused, to make up the unexplained shortfalls.

Stephen Mason, a retired barrister and editor of the practitioner text for judges and lawyers, Electronic Evidence, has been trying to persuade the legal profession for over a decade to take the subject seriously.

“The law presumes that computers are reliable. The defendant has to claim the system is not reliable, but they do not have any evidence,” he said. “This means it is impossible, especially when they are against an organisation with substantial financial means and the judge refuses to order disclosure of relevant materials to the defendant. This means those prosecuted have no means by which to effectively (or at all) challenge the reliability or integrity of a computer system. The government have said the presumption will remain. This has to change. Now.”

IT expert James Christie, added: “When the Law Commission recommended that computer evidence should be presumed to be reliable it wrote: ‘We are satisfied that the presumption of proper functioning … would be interpreted in such a way as to ensure (it) did not result in a conviction merely because the defence had failed to adduce evidence of malfunction which it was in no position to adduce.’

“After watching Mr Bates vs the Post Office, millions of people can see this was complacent nonsense. The presumption has ruined too many lives already. It must go, the sooner the better.”

Paul Marshall, a barrister who represented the subpostmasters who successfully overturned wrongful convictions by the Post Office, said given the enormous public interest generated by the recent ITV drama and documentary about the Post Office scandal, it appears the government will address the slow progress on overturning convictions and paying compensation.

But he added that it is an opportune time to reform the rule on computer evidence. “The time is surely now for both the government and the courts to address the other aspect, which is the wrong-headed asumption that evidence from a computer system is to be treated as accurate unless it is otherwise shown.”

He added: “This is something that has been flagged up extensively over the last few years.”

• Also watch: ITV’s Post Office scandal documentary: The real story •

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