Stuart Munro is Convener of the Law Society of Scotland's Criminal Law Committee and the head of Livingstone Brown’s Specialist Litigation Department. He acted for Susan Sinclair, the first subpostmaster in Scotland to have their conviction overturned on appeal. 

The broadcast of a major new drama on ITV, Mr Bates vs the Post Office, has brought the Post Office Horizon scandal into the spotlight like never before. But this is a scandal which has been brewing for many years.

What is the Horizon scandal all about?

The scandal concerns a computer system, Horizon, that was installed in post offices across the UK from 1999 onwards. The people who ran the post offices – in most cases known as subpostmasters – had to use the system to record all transactions. As with any accounting system, it had to be regularly reconciled. The system would flag how much money should be in the till, and any discrepancy with what was actually there would be highlighted.

Time and time again, Horizon identified supposed shortfalls, suggesting that money had gone missing. Sometimes the sums involved were small; sometimes they ran into the thousands. Audits were triggered. Allegations of embezzlement were made. Subpostmasters, who typically had no idea how any money could have gone missing, questioned the reliability of Horizon. They were told that the system was robust, and that nobody else had reported a problem. That wasn’t true.

Suddenly, subpostmasters were prevented from running their businesses. They were told that, under the contract they had signed, they had no choice but to pay the apparent shortfall to Post Office Limited. Many had to borrow money from family and friends. Their reputations and their finances were in ruin.

Then came prosecutions. In England, these were mainly run by Post Office Limited. In Scotland, where prosecutions can generally only be brought by the public prosecutor, these were the responsibility of the Procurator Fiscal. Those accused found it very hard to challenge the claims – the prosecution relied on an apparently robust computer system, which insisted that money had disappeared. Hundreds were convicted. Some went to jail; others received community based sentences. But a conviction for a crime of dishonesty can have an impact far beyond the sentence imposed. For one thing, it can make it almost impossible to get another job. Lives were destroyed.

As narrated in the ITV drama, it wasn’t until a number of subpostmasters won an English civil case in 2019 that the true scale of the injustice began to attract public attention. The judge determined that the Horizon system had numerous software errors and defects which were capable of causing the sort of apparent shortfalls that had led to the prosecutions. That decision opened the door to several convictions being overturned in the English criminal courts. A public inquiry was ordered; it continues to hear evidence, and has some way still to go.

Scotland has taken a long time to catch up. At the time of writing, only two Horizon convictions have been overturned. A few other cases are currently under consideration by the High Court. 

Why did this happen?

The public inquiry has been tasked with answering a range of questions, and identifying what key lessons must be learned for the future. The focus, understandably, is on the actions of Post Office Limited, who implemented the system, took action against subpostmasters, and – in England – conducted the prosecutions. 

From a Scottish perspective, particular issues arise:

  • Subpostmasters were told by investigators that nobody else had raised concerns about the reliability of Horizon. That wasn’t true. In Scotland, the fact that all such prosecutions were taken, and overseen, by the independent public prosecutor should have made this clear. Had it been, the concerns of subpostmasters would have carried more credibility, and proper investigations could have taken place at a much earlier stage.
  • Scots law requires criminal cases to be ‘corroborated’ – that is, evidence of guilt has to come from more than one source. Horizon cases typically involved charges of embezzlement – the dishonest appropriation of someone else’s money. Yet the only source of evidence that money had disappeared was Horizon. Why did the corroboration rule not act as a safeguard to those wrongly accused?
  • Post Office Limited acted not as prosecutor, but as a ‘Specialist Reporting Agency’ – essentially doing the job that would normally be done by the police. It had legal duties to reveal all relevant information to the Fiscal, but that didn’t appear to happen. To what extent did that contribute to wrongful convictions?
  • The Procurator Fiscal has a legal duty to disclose relevant information to those accused of crimes, and that duty continues even after a trial is concluded. As soon as the Fiscal became aware of concerns about the reliability of Horizon, that should have been disclosed. Yet it took until 2023 for the first Scottish convictions to be overturned, many years later.

There’s also a wider point, which has particular resonance as we move towards the increasing adoption of artificial intelligence (AI) systems. Fundamentally, subpostmasters were convicted because the evidence of a computer system was assumed to be robust and reliable. Protestations of innocence, even when nobody was able to say where the supposedly missing money had gone, were disbelieved. How could an accused person have any chance of persuading a court that a multi-million pound computer system, adopted by a major company, was defective?

If that happened with Horizon, why do we think it wouldn’t happen now? Our world is ever more technologically dependent. Computer systems are ever more interdependent. And unlike traditional applications, AI systems rely not just on their programming, but on their own ‘learning’. How could an accused person ever challenge the reliability of such a system? And how should the courts meaningfully deal with such a challenge?

What can those affected do?

It’s not definitively known how many people were affected by the Horizon scandal. Many hundreds of subpostmasters were prosecuted, including dozens in Scotland. Yet only a small proportion have had their convictions quashed; two so far in Scotland. 

Those who were wrongly convicted but who have yet to bring an appeal can still do so. In Scotland, late appeals can be brought with the permission of the High Court, or with the support of the Scottish Criminal Cases Review Commission (SCCRC, whose work prompted the first successful appeals).  The very first step is to speak to a lawyer.

Compensation is available to those affected. Different schemes have been set up by Post Office Limited, supported by the UK Government. These generally depend upon convictions being overturned. Given the life-long damage done to subpostmasters as a result of false claims and wrongful convictions, the value of claims can be considerable.

Again, getting early legal advice is crucial. Time limits apply to claims, so it is best to avoid any delay.

Criminal Law Committee

Advises the Council and the profession on criminal law matters.