Experts question court’s rejection of former Post Office manager’s Horizon appeal
Experts on the use of computer evidence question why Court of Appeal rejected former Post Office branch manager’s appeal against conviction
Experts have “cast doubt” on the judgment of the Court of Appeal over the conviction of a former Post Office branch manager who was refused his request to appeal his convictions for theft.
In a paper, experts discuss the evidence used by the prosecution in the 2007 conviction of David Cameron, a manager at England’s Lane Post Office in Hampstead, of 10 counts of stealing from customers. In 2022, the Court of Appeal didn’t consider it a “Horizon case”, yet the prosecution was reliant on evidence from the Post Office’s controversial computer system, they say.
The paper, authored by computer evidence experts Peter Bernard Ladkin and Harold Thimbleby with retired barrister Stephen Mason, argues that Cameron’s case is in fact a Horizon case.
Following the High Court revelations in 2019 that unexplained losses in Post Office branches were caused by errors in its Horizon computer system, the quashing of what were considered Horizon cases began at Southwark Crown Court and the Court of Appeal in December 2020 and April 2021 respectively. There have been hundreds more since as part of the Post Office Horizon scandal, which is considered one of the biggest miscarriages of justice in British history, but some appeals have been rejected on the grounds they are not related to Horizon errors.
Cameron made a request to appeal his convictions for theft. “He did not appeal within the time limit to do so, but after the 2019 revelations concerning the unreliability of Horizon accounting data, he applied to the Court of Appeal for leave to appeal (beyond the statutory time limit),” the paper’s authors told Computer Weekly.
But the Court of Appeal refused this in 2022 “primarily on the basis that his case was not a ‘Horizon case’ as they had previously defined it,” they added.
Cameron was convicted of 10 offences of theft, and was sentenced to nine months’ imprisonment, suspended for 18 months, and was made to carry out unpaid work.
The paper’s authors told Computer Weekly: “It seems to us to be a Horizon case because the entire collection of accounting data, including customer account statements, stemmed from Horizon accounting, and we know that (at the time) was flawed. Yet the Court of Appeal suggested that the presence of customer complainants somehow constituted evidence independent of Horizon. But neither we nor our colleagues can see how they reached that conclusion.
“The court declined his request, primarily on the basis that his case was not a Horizon case as they had previously defined it. In particular, the Court of Appeal said the presence of witnesses (customers of the England’s Lane Post Office) who said they had been defrauded showed there was evidence independent of Horizon to be considered.”
Rational reconstruction
Ladkin, Mason and Thimbleby attempt what they describe as a “rational reconstruction” of what could have happened during the alleged incidents, based on technical knowledge of the equipment and electronic-transaction protocols involved.
They said: “Contrary to the Court of Appeal, even the witness complaints derived from Horizon accounting data. Given the now-known unreliability of Horizon accounting (both in terms of numbers and in phantom transactions), we argue that this casts doubt on the safety of any of Mr. Cameron’s convictions.”
Posting on Bluesky about the paper, Alistair Kelman, a retired barrister and technologist, wrote: “Another tranche of major miscarriages of justice like the Post Office Horizon cases. Three distinguished lawyer/technologists show that the UK Court of Appeal has been rejecting appeals based on the exact same evidence from the Post Office Horizon IT System.”
Since Cameron’s request to appeal his conviction in 2022, the Post Office scandal has hit the mainstream. Following intense public pressure, the government introduced legislation to overturn more than 700 prosecutions which were based on data from the Horizon system.
Read the paper here: Misunderstanding digital computer technology in court: A commentary on a case involving the Post Office Horizon system.
Computer Weekly first exposed the scandal in 2009, revealing the stories of seven subpostmasters and the problems they suffered due to Horizon accounting software, which led to the most widespread miscarriage of justice in British history (see below timeline of Computer Weekly articles about the scandal since 2009).
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