Any doubt about the reliability of the UK Post Office’s Horizon IT system “would have seriously affected the decision” to prosecute hundreds of subpostmasters, a former prosecutor has testified as an investigator recalled Post Office managers “constantly” touting Horizon’s reliability despite its known issues.

Investigators had a “duty of candour” and were relied upon to conduct thorough investigations into allegations that subpostmasters had committed fraud and false accounting, former Scottish Procurator Fiscal (PF) David Teale – who as PF from 2000 to 2015 oversaw the prosecution of around 100 Scottish subpostmasters – testified to the UK government’s ongoing Post Office Horizon IT Inquiry.

Yet with “no specific guidance” provided about how Post Office investigations should be evaluated by the PF – a statutory agent who decides whether the evidence provided to it warrants a criminal prosecution – and no safeguards to ensure that investigators were getting the full picture, Teale agreed that the PF “would have to take it on trust that everything was being done correctly by all investigators, in all cases.”

“It’s certainly got the potential for problems arising if there is a lack of candour,” he said. “If the reporting officer had known that there was some doubt generally about the accuracy of the Horizon system, then there should have been the sort of doubt that came to light later on.”

Evidence given during the hearing has, however, painted a picture of a self-protecting Post Office that went out of its way to collude with Fujitsu – which developed the system in the 1990s to manage Post Office Limited’s (POL) approximately 18,000 branches across the British Isles – ultimately railroading through the prosecutions of over 700 subpostmasters who were fined, jailed, ostracised by their communities and often financially ruined.

Investigators were insulated from Fujitsu’s investigations into Horizon bugs, however, with Northern Ireland’s only POL investigator, Suzanne Winter, testifying that senior POL managers “constantly” reiterated the systems’ reliability to staff and reporting that investigators “didn’t have access to anyone in Fujitsu” to help them look into subpostmasters’ concerns about the system’s problems.

Investigators requesting detailed ARQ audit data had to raise a request through their supervisors, who would escalate it to Fujitsu for processing that could take weeks – and with investigators limited to making a few requests per month, Winter said there was a pervasive sense that the integrity of Horizon was taken as sacrosanct inside POL and Fujitsu.

Fujitsu “were being reported as the expert of the computer and you were more or less [unable to question that],” she explained. “You didn’t feel you could challenge anything. You just got the impression that if you started to challenge too much, it didn’t go well.”

A “self-policing” culture of secrecy

Winter’s testimony – which corroborates previous evidence from investigators that requests for review of Horizon data were routinely ignored, that Fujitsu colluded with POL to blame subpostmasters for audit shortfalls, and that Fujitsu helped convict subpostmasters to gloss over issues with Horizon – was the latest in a string of allegations exposing a cult of secrecy about Horizon within POL.

The UK government is reportedly “taking seriously” new BBC allegations that in April 2014, a POL board subcommittee decided to bury a report by forensic accountancy firm Second Sight that identified bugs in Horizon – with minutes showing that the group discussed “options to support [Second Sight] or reduce their role” amidst concerns that the audit report could make them criminally liable for the subpostmasters’ convictions.

POL chair Henry Staunton was forced out over the weekend, as the expanding scandal – which gained new life in January with the airing of a documentary that was recently picked up for Australian broadcast in February – saw former subpostmistress Kathleen Crane exonerated 14 years after she was convicted of fraud, given a 12-month community order, and ordered to repay over $34,600 (£18,000) she was alleged to have stolen from POL.

Dozens of convictions have now been quashed and hundreds more are being fast-tracked as the UK government works to fix the long-running miscarriage of justice, which played out over more than a decade as POL sicced Winter, and her fellow investigators across the UK, on one subpostmaster after another.

Officers were relied upon to ensure the accuracy of their data, with the PF relying on “self-policing” and making the them aware of any factual issues or evidentiary shortcomings in their reports.

Yet as the POL investigations dominated the work of investigators like Raymond Grant – who estimates he spent 65 to 70 per cent of his time investigating accused subpostmasters – those investigators were rated by POL on their efficiency, effectiveness, and success in recovering funds from subjects.

Even where investigators did seek assurances about the integrity of Horizon and the ARQ audit data, the consistent story that Horizon was infallible meant that their reports failed to convey potential issues with the system to PFs.

This led Teale, who said the PF is “entitled to expect that the reporting officer will have satisfied themselves as to the reliability [of evidence],” to pursue the prosecution of subpostmasters including William Quarm, who pled guilty in 2010 to avoid a prison term and died in 2012 long before he could be exonerated.