There is a case in the news at the moment about the post office securing 736 convictions for false accounting and theft that later some were overturned on the basis of an accounting error made by an internal computer system. The High Court described the computer system as not "remotely robust" for the first 10 years of its use, and still had problems after that.

What I would have expected to happen in this case would be for the accused to request the data on which the decision was made during discovery, with an accountant compared this to their own records and demonstrated an error. It appears this did not happen, though it is hard to find what actually did happen.

Do we know what happened here? It it possible for a party to such a suit to bring evidence to the court without providing the underlying data to the other party?


2 Answers 2


(As there are cases that remain sub judice, I will give only a general answer describing the disclosure process.)

How does discovery disclosure work for financial crimes?

Disclosure for all criminal investigations in England and Wales, including those in to financial crime, are carried out in accordance with Parts 1 and 2 of the Criminal Procedure and Investigations Act 1996 and its accompanying Code of Practice.

A full explanation is given in the Code, but put briefly: the police appoint a Disclosure Officer whose role includes reviewing and assessing everything held by the police, called "material", and passing details of all "relevant material" to the CPS appointed prosecutor.

There are four stages in the police disclosure process, called the 4Rs:

  • Record
  • Retain
  • Review
  • Reveal

These 4Rs overlap with three questions that require answering in order:

  • Record and Retain:

Q1: Is it "relevant material" to the investigation? If No, nothing further need be done. If Yes then Record and Retain it in a "durable and retrievable format" - write it down, save it to disc etc, keep it safe and in a place where it can be found.

  • Review:

Q2: Is it "sensitive material"? e.g. does it relate to informants, covert tactics, information given in confidence etc? Either way, two seperate schedules of relevant material according to its "sensitivity" are created.

  • Reveal:

The Disclosure Officer passes both schedules (and the actual material if necessary) to the CPS prosecutor who provides the defence with a copy of the non-sensitive schedule. The prosecutor also asks:

Q3: Does the material "undermine the case for the prosecution or assist the defence with theirs"?  If No, nothing further need be done.  If Yes, the prosecutor must disclose the material to defence, unless it sensitive and giving it to the defence is not, for example, in the public interest as it may jeopardise life, covert operations etc. The prosecutor and police then has to decide whether to drop the case or not in order to protect the reason for the sensitivity. (They may also apply to the Crown Court judge for a Public Interest Immunity certificate which - in very, very rare cases - allows a trial to go ahead in the interests of justice without the defence being made aware of material that may assist their case as long as the whole trial process is fair to the defendant.)

The defence, in addition to their copy of the non-sensitive schedule, can apply for sight or copies of and any material that they consider also undermines or assists but has not been disclosed to them by the prosecutor, and is necessary for their case. In the first instance this application is to the CPS prosecutor, but if it is refused the defence may apply to the trial judge for a ruling on whether it must be disclosed or not.

The overriding principle is ensuring a fair trial.


It it possible for a party to such a suit to bring evidence to the court without providing the underlying data to the other party?

It is possible but the principles of a fair trial, disclosure and the continuity of evidence (what some call the chain of custody) coupled with challeges by the defence are supposed to ensure that the provenance and accuracy of evidence is properly tested and accountable at a Plea and Trial Preparation Hearing (PTPH) before a trial opens. Unfortunately, especially in highly complex investigations, this does not always seem to be the case.


The other answer sets out the general principles of disclosure in criminal cases. In the 42 cases dealt with in Hamilton v Post Office Ltd [2021] EWCA Crim 577, we also know “what actually did happen.” The Post Office’s failure to comply with its disclosure obligations caused the Court of Appeal to set aside the appellants’ convictions, even though most of them pleaded guilty:

It was POL's clear duty to investigate all reasonable lines of enquiry, to consider disclosure and to make disclosure to the appellants of anything which might reasonably be considered to undermine its case. Yet it does not appear that POL adequately considered or made relevant disclosure of problems with or concerns about Horizon in any of the cases at any point during that period …

… the failures of investigation and disclosure were in our judgment so egregious as to make the prosecution of any of the “Horizon cases” an affront to the conscience of the court. By representing Horizon as reliable, and refusing to countenance any suggestion to the contrary, POL effectively sought to reverse the burden of proof: it treated what was no more than a shortfall shown by an unreliable accounting system as an incontrovertible loss, and proceeded as if it were for the accused to prove that no such loss had occurred. Denied any disclosure of material capable of undermining the prosecution case, defendants were inevitably unable to discharge that improper burden.

At least one appellant instructed his own experts, but apparently decided that challenging the system’s reliability with the material and resources available to him was unlikely to succeed at trial:

Defence accounting and IT experts were instructed. Detailed disclosure requests were made in respect of Horizon and its underlying data. It appears that POL disclosed full ARQ data as well as details of the relevant Horizon transactions and logs of calls to the Horizon Helpline. On the other side of the scales, statements from Fujitsu employees attested to Horizon's reliability. Ultimately, the issue of Horizon's unreliability was not pursued at trial – possibly because the defence experts had struggled to understand the Horizon system.

Much more can be learned about the general principles, internal failures of the Post Office and circumstances of individual appellants by searching the 92-page decision for the keyword “disclosure.”

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