BCS demands reform to rules on computer evidence following Post Office Horizon scandal revelations

BCS, The Chartered Institute for IT, has called for reform to the way computer evidence is treated in courts, following the wrongful prosecutions of subpostmasters.

The IT professional body also wants the government’s statutory inquiry into the scandal to consider the current rules on digital evidence.

“We are calling for a swift review of how computer evidence is treated by the courts,” said Paul Fletcher, CEO at the BCS.

From 2000 for a period of 15 years, the Post Office blamed subpostmasters for unexplained shortfalls in their accounts. It used evidence from the Horizon retail and accounting system, which subpostmasters use in branches, to prosecute those that could not account for shortfalls.

But the subpostmasters claimed the Horizon system was to blame, because the shortfalls only started after Horizon was introduced in 1999/2000. They were proved right in a High Court group litigation order in 2019.

A total of 736 subpostmasters were prosecuted based on Horizon data, with some sent to prison, many made bankrupt and families ruined. A total of 47 former subpostmasters recently had their criminal records quashed after years of campaigning, and hundreds more could follow.

The Post Office was able to prosecute the subpostmasters using Horizon evidence, despite its errors, because of a change in court rules concerning computer evidence, which came into force in 1999.

Before then, prosecutors who relied on digital evidence in court had to prove that the computer system had worked as it should. However, the change to the rules that year meant it was now presumed that the computer system worked correctly unless there was explicit evidence to the contrary.

Fletcher said this should not be the case and organisations that relied on data from computer systems to support prosecutions should be required to prove the integrity of that data.

BCS said it wants an “end to the legal presumption that computer systems data is always correct, with no burden on the prosecution to prove it”.

Earlier this month, the Post Office contacted a further 540 former subpostmasters informing them that it might have wrongly prosecuted them using unreliable computer evidence.

Fletcher added: “The Horizon case uncovered a range of issues that are key to the reputation of our industry, including the relationship between technology and organisational culture, as well as the vital importance of meeting independent standards of professionalism, trust and ethics.”

Computer Weekly first revealed the scandal in 2009 with the stories of seven subpostmasters (see timeline below of Computer Weekly articles since 2009).

Sam De Silva, partner at international law firm CMS and chair of the BCS’s Law Specialist Group, said the Post Office scandal highlights the dangers of accepting the output of automated systems without question.

“It was for the subpostmasters to prove that the outputs and logs from the computer system were flawed or not accurate,” said De Silva. “Yet how could non-IT specialists be expected to prove this when even some experienced IT professionals would find it a challenge to do so?”