At a recent public inquiry about the Post Office scandal, John Bartlett, the Post Office’s director of assurance and complex investigations, spoke out. He indicated that the rules around computer evidence might revert to the standards that existed before the 1999 changes.
In 1999, a legal presumption came into play that stated computer systems were working correctly unless proven otherwise. This new rule followed recommendations from the Law Commission and replaced the previous requirement from the 1984 PACE Act, which demanded proof of a computer’s proper operation. This shift to presuming accuracy largely benefited the Post Office, allowing it to criminally charge subpostmasters based on data from the Horizon system. Many subpostmasters were wrongfully convicted of theft and false accounting due to unexplained losses tied to that data.
When the Horizon system flagged shortfalls after its rollout in 1999, subpostmasters often faced prosecution. Courts accepted the assumption the software was reliable, but this was later challenged. A group litigation order in 2018/19 revealed that 555 subpostmasters demonstrated the Horizon system’s flaws and questioned its reliability.
Since a dramatized version of the scandal aired on ITV, many former subpostmasters have either overturned convictions or are in the process of having them quashed. Legal and technology experts have pushed for changes to the presumption around computer evidence for years, and the scandal has brought this issue to the forefront.
Bartlett, who has a background in law enforcement, mentioned, “This scandal has shown that the assumption that digital systems can be relied on needs reevaluation.” He reflected on his early police days, where there was no automatic trust in computer systems. He expects law enforcement will revert to old practices, conducting verification exercises on digital data for all cases, not just those related to the Post Office.
Interestingly, the Post Office backed the 1999 rule changes. In a letter to the Law Commission back in 1995, they expressed that the earlier rules made prosecutions overly challenging, particularly for cases involving subpostmasters. They stated that computer evidence should be treated like any other evidence, suggesting a presumption of accuracy unless disproven.
The Post Office’s stance essentially highlighted their need for presuming computer evidence as reliable to streamline prosecutions. However, it’s now clear that the Horizon software produced inaccurate data, leading to the wrongful convictions of hundreds—a situation now recognized as one of the largest miscarriages of justice in British history.
The scandal first came to light in 2009, thanks to coverage from Computer Weekly, which reported on the struggles of subpostmasters grappling with the flawed Horizon accounting software.