In 1999, a new rule was introduced regarding the use of computer evidence in court, which inadvertently allowed the Post Office to prosecute and ruin the lives of innocent postal managers.
It was several years earlier, in 1995, that the Law Commission called for evidence on a proposed change to section 69 of the Police and Criminal Evidence Act 1984, which stated that computer evidence must be subject to proof that the computer system was operating correctly at the time of the alleged offence.
The Law Commission wanted to hear feedback on proposals to change this and introduce presumption that a computer system is operating correctly unless there is clear evidence to the contrary.
The 1995 consultation sought the views of prosecutors on proposed changes to the rules for the use of computer evidence in court. One such organization was the post office. In its response, the Post Office's criminal justice department said the rule at the time was “somewhat burdensome from a prosecution perspective” and that it supported the change.
The Postal Service's legal representative wrote: “I believe that computer evidence is no different in principle from any other evidence and should be generally admissible so that any argument at trial will be based on its weight rather than its admissibility.
“So I think there should be a presumption that the car is in working order, etc., and if the defense wants to argue otherwise, then obviously they should be able to do so. So at this time, I think the evidentiary requirements are too stringent and may make it difficult to prosecute.”
Read more: The Post Office supported a 1999 law change that made it easier to prosecute using computer evidence..
Legal rule as a business tool
The rule was introduced in 1999, which coincided with the introduction of the Horizon system, which automates the accounting of the entire postal branch network.
Soon after, the post office began to go on a rampage. He already had private prosecution powers and did not need the police or the Crown Prosecution Service. Now he didn't need hard evidence, just evidence of his faulty computer system.
In the seven years between 1991 and the year before Horizon, an average of six subpostmasters or employees were convicted per year. This is a 766% increase in the number of criminal cases.
The Post Office threatened legal action for forcing postal deputies to cover an unexplained shortage that didn't actually exist. This was made easier because the Post Office did not have to prove that Horizon was operating during the shortage.
Read more: IT scandal exposes legal rule that made it easier for the Post Office to prosecute innocent people.
Supreme Court raises questions
The controversial rule, as well as the Postal Department's private prosecution powers, became major talking points after The High Court battle between postmasters and the Post Office has ended in December 2019. This Class Litigation Order (GLO) proved that the accounting deficiencies blamed on the subpostmasters were in fact caused by computer errors.
Soon after, in June 2020, convictions against the sub-postmasters based on Horizon evidence were sent to the Court of Appeal. In the meantime, the government has been asked to review the rules regarding private prosecution.
Government agrees revision
Post Office scandal sets legal guidelines, including government decision overturn the convictions of hundreds of people who were prosecuted based on Horizon data. Less dramatically, but of great significance, private prosecutions were dropped.
However, the rules regarding evidence remain the same. In 2023, after a large number of subpostmaster convictions were overturned, a parliamentary campaign to change the rules on computer evidence began to gain momentum.
Read more: Lawmaker calls for review of computer evidence rule that led to postmasters being wrongly convicted.
Social pressure
Things accelerated in January 2024 with the airing of an ITV drama about the post office scandal. Nothing new was revealed, but the harrowing stories of the postmasters reached the general public rather than the campaigners and a few journalists.
Everyone knows the profound impact this drama had: the government moved quickly to overturn the postmasters' convictions, but it also led to greater urgency for computer evidence rules that allowed the Post Office to prosecute subpostmasters without strong or flimsy evidence.
Read more: Change in rules on computer evidence will be 'resulting' from Post Office scandal.
Read more: Lords debate amendment to computer evidence law in light of Post Office scandal.
Call for evidence
It was January 2025 when the government turned to experts to help it understand what needed to change – a move that was welcomed by people affected by the current rules.
Read more: Government calls on experts to weigh in on computer evidence to learn from Post Office scandal.
Overhaul of legal rule on computer evidence is long overdue, victims of Post Office scandal say.
Computer and legal experts answer the call to weigh in on computer evidence.
What will appear?
According to the Court of Appeal, it's not that simple Judge Peter Fraserwho led the High Court battle between the Post Office and sub-postmasters in 2018/19: “It is very difficult now to understand how courts in the future, in the next 10, 20, 30 years, will deal with computer evidence, or evidence obtained by computers, or evidence about the operation of computers. It is important to recognize what can be changed.
“Some flexibility is needed in the approach to this because the current complexity will become more and more noticeable,” he said in a conversation in the Inner Temple, Use of electronic evidence in legislation.
Read more: There is no easy replacement for digital evidence rules, Post Office Horizon judge says.
What lawyers and IT experts say
Alistair Kelman, British lawyer (retired) and technologist: How to solve the problem of computer evidence.
James Christie, independent consultant and IT expert: Law Commission misrepresented expert opinion when it changed computer evidence rule.
Stephen Mason, retired lawyer and digital evidence expert: The reason for the Horizon Post Office scandal? Legal commission? Judges? Lawyers?
Paul Marshall, a lawyer who has represented former postmasters: The naivety of computer evidence leaves the door ajar for more miscarriages of justice.
Stephen Castell, computer software and systems expert, witness: A trial based on computer evidence must begin with an examination of the computer evidence..
