The cause of the Post Office Horizon scandal? The Law Commission? Judges? Lawyers?

The appropriateness of the current law on the use of computer evidence in court is under the spotlight following Post Office scandal revelations

Stephen Mason

Published: 01 Nov 2023

From 1999, Post Office Limited prosecuted subpostmasters, subpostmistresses and employees for theft and fraud based on evidence produced by the Horizon computer system, which appeared to show shortfalls in their branch accounts. Hundreds were convicted, sentenced to terms of imprisonment, fined, or had their property confiscated. Lee Castleton was made bankrupt after attempting to challenge the Post Office in a civil case.

The Post Office Horizon IT Inquiry under the chairmanship of Sir Wyn Williams has begun to expose the lies, mismanagement, racism, and disregard for the truth exhibited by the Post Office, including employees signing statements of truth that were not true.

The responsibility to prosecute firmly rests on those employees and external lawyers who were in control of the process. Some were also responsible for the cynical and shocking manipulation of false evidence.

There are three important issues that sit at the heart of the failure of the legal system.

The presumption that computers operate correctly

The Post Office relied on the presumption that computers were operating correctly. In England and Wales, as a matter of law, computers are considered to have been working correctly unless there is evidence to the contrary (see chapter 5 in the legal practitioner text Electronic Evidence and Electronic Signatures). This means that evidence produced by computers is treated as reliable unless other evidence suggests otherwise. This way of handling evidence is known as a ‘rebuttable presumption’. A court will treat evidence from a computer or computer system or systems as if it – or the systems – works perfectly unless someone can show why that is not the case. It is for the defence to raise the issue of reliability.

This presumption poses a significant hurdle to those who dispute evidence produced by a computer system or systems. The challenge is usually insurmountable. This was the issue in the trial of Seema Misra.

The presumption was finally revealed as being false in the December 2019 judgment in the group litigation Bates v The Post Office Ltd (No 6: Horizon Issues) Rev 1, where Mr Justice Fraser concluded (paragraph 968) that it was possible that software errors in Horizon could have caused apparent shortfalls in branch accounts, rather than these being due to theft or fraud.

The legal presumption, as applied in practice, has exposed widespread misunderstanding about the nature of computer failures. Errors in computer systems, specifically software defects (bugs), may not be readily apparent and can be difficult to identify. Bugs may cause a computer system to work differently from the intended behaviour, with unexpected – sometimes devastating – consequences. The effects of bugs in the Post Office Horizon computer system were not readily observable or identifiable to subpostmasters and others prosecuted by the Post Office.

This means that those prosecuted could not effectively (or at all) challenge the reliability or integrity of the Horizon computer system. They had no means of providing evidence to the court capable of rebutting the presumption. In practice, rebutting the legal presumption presents insuperable and costly problems for defendants.

It is unknown how many other prosecutions will have been affected by the presumption. The fact that a computer has failed may well not be obvious. Professors Ladkin, Littlewood, Thimbleby and Thomas have written eloquently about this, and further articles have been written by Professor Ladkin and James Christie.

The Law Commission has a lot to answer when recommending the repeal of section 69 of the Police and Criminal Evidence Act 1984 and replacing it with the presumption that computers are reliable. As James Christie has demonstrated (page 62 of his recent article ‘The Law Commission and section 69 of the Police and Criminal Evidence Act 1984’.

‘A study of the papers and articles quoted in the consultation paper and final report reveals that the Law Commission misunderstood, or misrepresented, the opinions of the main sources cited as being in favour of repeal. The Law Commission failed to address the strongest arguments against repeal without replacement, …. It ignored the advice of the experts they cited who all argued that the focus of courts should be on the reliability of computer evidence, …. The Law Commission’s comments and conclusions revealed that they had not understood the nature of computers and complex software systems as described in the sources upon which they relied.’

The Crown Prosecution Service, Director of Public Prosecutions and Post Office wanted section 69 to be repealed and the presumption to be introduced. The question for the Law Commission is this: why did it misrepresent the comments of experts to introduce the presumption? Was it to comply with these requests?

Education and knowledge of judges and lawyers

Second, the Post Office might not have succeeded in their prosecutions if the lawyers and judges had been educated in electronic evidence. The Bar Standards Board Handbook contains the rules about how barristers must behave and work. It also contains the Code of Conduct for barristers. Item gC39 says:

‘In order to be able to provide a competent standard of work, you should keep your professional knowledge and skills up to date, regularly take part in professional development and educational activities that maintain and further develop your competence and performance …’

A practitioner text, entitled Electronic Evidence written for lawyers, judges and legal academics was first published in 2007. It is now in the fifth edition. The legal profession should not ignore this topic (see Denise Wong and Deveral Capps).

The importance of disclosure

Third, disclosure is the requirement that each party in litigation is required to make available to the other party documents that are relevant to the issues in dispute. Where a party refuses to provide relevant documents, the other party can apply to a judge for an order that they provide the documents. This is an important and powerful power. Seema Misra’s defence was made impossible because requests by her lawyers for disclosure of the computer system was refused four times by three judges. By comparison, Mr Justice Fraser made disclosure orders to the Post Office, which revealed many incriminating documents.

The future of the presumption

The government intend to retain the presumption that computers are reliable, as stated by James Cartlidge, Parliamentary Under Secretary of State (Ministry of Justice), on 17 May 2022.

Were it not for the group litigation initiated by Alan Bates and Justice for Subpostmaster Alliance, the unreliability of the software in the Post Office’s Horizon computer system might not have been revealed. Previous challenges to Horizon’s correctness could not rebut the presumption of reliability for computer evidence. The financial risk of bringing legal action deterred other challenges. Similar issues apply where the reliability of computer evidence is questioned, such as in payment disputes and motor vehicle accidents.

The presumption has been the cause of widespread injustice.

The finder of fact acts as a moral agent, and central to this is that the findings by a court must be justifiable and meet the demands of rationality and ethics. After all, the legal system is supposed to be about fairness and justice, isn’t it? And as Professor Moorhead writes, it’s also about the ethics of good chaps, isn’t it?

The question is: When will those responsible demonstrate they understand the need for change, in the interests of justice?

Stephen Mason (photo credit: Dainka Stoilova)

Stephen Mason is a retired barrister, joint editor, with Professor Daniel Seng, of Electronic Evidence and Electronic Signatures (5th edition, 2021), open source and editor of International Electronic Evidence (2008). He founded the open-source international journal Digital Evidence and Electronic Signature Law Review, which has become an international focal point for researchers in the area.