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Just how did the Post Office miscarriage of justice happen and why did it take so long to unravel?

On 23 April 2021 the Court of Appeal quashed the convictions of 39 former sub postmasters and postmistresses (SPMs) righting one of the largest miscarriages of justice in English legal history.


The former SPMs all ran local branch post offices and, between 2003 and 2013, were accused and convicted of various criminal offences ranging from theft and fraud to false accounting, in private prosecutions brought by their employer, the Post Office. Their prosecutions were largely based on discrepancies raised by a faulty computer system, Horizon, which the Post Office refused to accept could be wrong.

Understandably, the convictions had a devastating effect on the lives of the SPMs with all receiving criminal records and some receiving prison sentences. Aside from the sanctions imposed by the court, the SPMs faced the stigma of criminal convictions of dishonesty and suffered a resulting loss of reputation, with many struggling to find employment following their conviction and some declaring bankruptcy.  Three of the SPMs did not live long enough to see their names cleared.

The Horizon computer system

Central to the Post Office prosecution was information obtained from Horizon, an electronic accounting system implemented in Post Office branches from 1999. The Horizon system was supposed to record all transactions at a branch and provide information about how much stock and cash should be held at a branch. If there was a discrepancy between the amount of cash and stock held at a branch and the amount stated by Horizon, the SPMs were under a contractual obligation to make good the difference. SPMs had to use the Horizon system, and there was no system in place to dispute the figures provided by Horizon. However, from its implementation, SPMs reported issues with the system, citing discrepancies and shortfalls that they were unable to explain. The Post Office was also made aware of reports of phantom sales and of a number of bugs within Horizon.

Failures of the Post Office and a continuation to prosecute

Despite these reports of errors and some awareness of bugs within Horizon, the Post Office continued to assert that there were no faults with the system. It maintained that the only explanation for the shortfalls was the dishonesty, negligence and/or incompetence of the SPMs. Between 2000 and 2014, the Post Office prosecuted 736 SPMs for alleged losses totalling £18 Million.

The turning point in this matter was a High Court hearing in December 2019. It found that the Post Office had failed to investigate the reported issues with Horizon, despite evidence indicating that the system was faulty, and had deliberately attempted to suppress information that questioned the reliability of Horizon. In his judgement, Frazer J outlined not only evidence of various bugs but also numerous examples of internal documents which showed that the Post Office had “at least to some degree an awareness of Horizon Problems”. The judge stated that the approach of the Post Office:

“demonstrates a simple institutional obstinacy or refusal to consider any possible alternatives to their view of Horizon which was maintained regardless of the weight of factual evidence to the contrary”.

It was the findings of fact in this High Court hearing that lead to the Court of Appeal (COA) hearing.

Court of Appeal Hearing

The Appellants argued in the COA that the knowledge and failure to investigate the issues with Horizon raised questions as to whether the Post Office had adequately undertaken its duties of investigation and disclosure under the Criminal Procedure and Investigations Act 1996.

S3 of the Criminal Procedure and Investigations Act 1996 states that a prosecutor must disclose:

“any material which has not previously been disclosed to the accused and which might reasonably be considered capable of undermining the case for the prosecution against the accused or of assisting the case for the accused.”

The Appellants appealed against their convictions on the basis that these failures of investigation and disclosure, had they been known at the time, would have enabled them to mount a successful application to stay their prosecutions.

The COA summarised the two main grounds of appeal on which the criminal proceedings brought by the Post Office abused the process of the court as follows:

“Ground 1: the reliability of Horizon data was essential to the prosecution and, in the light of all the evidence including Fraser J’s findings in the High Court, it was not possible for the trial process to be fair;

Ground 2: the evidence, together with Fraser J’s findings, shows that it was an affront to the public conscience for the appellants to face prosecution.”

In its judgement against the Post Office, the COA overturned the convictions of the 39 appellants finding both Ground 1 and 2 abuse and stating that the Post Office had sought to “avoid legal obligations when fulfilment of these obligations would be inconvenient and/or costly”.

The COA held that the Post Office knew of problems with Horizon, knew that SPMs across the country had been complaining of discrepancies and knew of various bugs and errors that had been discovered.  In not making this information available during the prosecution, they had “prevented the appellants from challenging, or challenging effectively, the reliability of the data” on which their prosecutions were based.

It was held that these “pervasive failures of investigation and disclosure went in each case to the very heart of the prosecution” and, in failing to discharge these duties, the Post Office had prevented the SPMs from having a fair trial based on the issue of whether the Horizon data was reliable.

What happens next?

The UK government has launched an enquiry into the Horizon scandal; however, this enquiry is currently only looking at the Horizon system itself and not the role of the Post Office as a prosecutor. There have been calls to expand the scope of the enquiry so that it considers the role of the Post Office as a prosecutor and the subsequent criminal proceedings, but thus far these have been rejected by the UK government.

The Post Office has stated that it is in the process of contacting those who it believes may have been the victim of a miscarriage of justice.


This briefing is for guidance purposes only. RadcliffesLeBrasseur LLP accepts no responsibility or liability whatsoever for any action taken or not taken in relation to this note and recommends that appropriate legal advice be taken having regard to a client's own particular circumstances.

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