Bugs in the UK Post Office’s Horizon system caused so many accounting mistakes that prosecutors could find no explanation other than deliberate fraud, one lawyers has revealed while confirming he had been given “no reason to believe” Horizon was flawed.

Speaking during testimony to the UK Post Office Horizon IT Inquiry, former prosecutor Kevin Shiels – who in 2004 prosecuted former subpostmistress Maureen McKelvey in his role as a Northern Ireland prosecutor – said that, had there been any intimation that computer error caused the shortfalls for which she was blamed, McKelvey’s case might have failed the Test for Prosecution, a judicial standard that requires both that the evidence that can be presented in court is sufficient to provide a reasonable prospect of conviction, and that prosecution is required in the public interest.

Yet in weighing the evidence against McKelvey – who was tried for fraud but cleared by a jury five years after being fired by Post Office Limited (POL) – “there was nothing [in disclosures by investigators] which alerted me to any issue with the Horizon IT system,” Shiels said in his witness statement as he explained how the decision was made to prosecute McKelvey.

Before the 1999 introduction of the Horizon system – which was developed by Fujitsu and has been blamed for what some are calling the UK’s worst ever miscarriage of justice – McKelvey said that her dealings at her Post Office branch had raised no concerns and that “I would be audited yearly with no issues”.

After Horizon was introduced, however, McKelvey began seeing alleged shortfalls of $97 (£50) to $385 (£200) per week – drawing a “terrifying and humiliating” audit by “Mafia-like” Post Office auditors in which she recalled “being treated with utter contempt.”

In reviewing the evidence briefs while weighing her prosecution, Shiels testified, “because of the amount of alleged human errors, there were too many to discount as solely errors and not a deliberate act or deliberate acts of theft… It just couldn’t simply be incompetence on behalf of Mrs McKelvey. There must have been something more.”

As it turns out, the “something more” was a systemic pattern of bugs in Horizon that led to more than 700 former subpostmasters – small business owners running Post Office shops in many of the UK’s most remote places – being prosecuted, fined, jailed and even dying during a long-running cover-up in which Fujitsu colluded with POL to fudge evidence and shift blame away from its own faulty system.

Investigators were “constantly” told of the system’s reliability despite a growing tide of internal concern about its workings – but with individual subpostmasters’ concerns and requests for information routinely ignored, Shiels reported that not even McKelvey’s own defence team tried to blame the Horizon system for the shortfalls.

“Had any matter been brought to my attention suggesting that there was a question mark over the reliability of the Horizon IT system,” he testified, “this would have been disclosed as it would clearly have undermined the prosecution case.

“If such a matter was brought to my attention, I would have viewed it as disclosable and taken the appropriate steps [and] I would have reviewed whether the Test for Prosecution remained met.”

Creatures of habit

Testimony at the ongoing inquiry has shown investigators, auditors, and prosecutors were repeatedly kept in the dark about alleged problems with Horizon – or that POL management had, as was recently revealed by the BBC, actively worked to bury those problems to avoid litigation for hundreds of false prosecutions.

“In the limited time I was involved with Horizon, I had no knowledge of any problems with the accuracy of the Horizon system,” said Frederick Leslie Thorpe, a Post Office investigations team manager.

In the first few years of Horizon’s rollout “information regarding the alleged irregularities would be gathered, usually from external sources, from retail network managers, from auditors,” Thorpe said. “Horizon was in its infancy and we were still operating the paper-based system.”

“We’d never been given a direct contact and it was not common practice to contact [Fujitsu] for more information,” he added – echoing previous claims by one of Thorpe’s reports, Northern Ireland investigator Suzanne Winter, that “you didn’t feel you could challenge anything” about Horizon’s reliability.

Cursory training introduced investigators to the system but offered no hands-on experience, Thorpe revealed, with only “very, very basic” guidance about how the system worked or how investigators might use it or get information about it.

The teams were left to decide how to present cases to the police for prosecution, Thorpe said, adding that “by the time we were getting to the point of submitting cases [for police consideration] there was really nobody to actually talk with within the Post Office” who might have shared information about Horizon’s problems.

That left investigators to develop procedures for interviews of subpostmasters with minimal guidance – so when McKelvey suggested during her interview that there might have been an error on the computer, Thorpe took it as a throwaway comment rather than a possible investigative lead.

“There was no real suggestion that Horizon was in any way at fault in this,” he testified while admitting that McKelvey’s suggestion “perhaps should have been explored slightly further in that particular instance.”

The recent interest in the Fujitsu Horizon Post Office scandal was ignited by the television series, Mr Bates vs The Post Office which screened in the UK earlier this year. In Australia, the series will be screened by Channel 7 and 7 Plus at 8.30pm on Wednesday 14 February, concluding Wednesday 21 February 2024.