I was reading the following academic paper. At the very beginning, it mentions that under the Law in England & Wales, a computer is presumed to be operating correctly.

This is the line I am interested in:

"In England and Wales, courts consider computers, as a matter of law, to have been working correctly unless there is evidence to the contrary."

Does someone have a link (preferably a reputable link) where I can investigate this Legal Rule, that was mentioned in that academic paper?

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    Is this not answered by the paper in question: It proposed that s69 should be repealed (and not replaced) with the effect that: ‘In the absence of evidence to the contrary, the courts will presume that mechanical instruments were in order at the material time. The Law Commission considered that the words ‘mechanical instruments’ would extend (by default) to include computers. Section 69 of PACE 1984 was repealed by the Youth Justice and Criminal Evidence Act 1999. The result was that the law makes the presumption that the Law Commission identified and recommended.
    – User65535
    Dec 10, 2023 at 10:44
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    @User65535 I think you misunderstood. I want a source to the Legal Rule which states that computer are presumed to be working correctly, unless evidence is brought forward to show it was not working properly. Dec 10, 2023 at 10:48
  • 1
    There's a recent discussion at davidallengreen.com/2023/09/…
    – user20637
    Dec 10, 2023 at 20:10
  • 2
    Those caught up in the Post Office's Horizon software scandal certainly didn't believe the computers to be infallible... the problem is that the Post Office did believe them to be working correctly.
    – TripeHound
    Dec 10, 2023 at 21:22

1 Answer 1


The article itself answers the question, albeit not in the most direct way. It cites Law Commission (England & Wales) Report No LC245 (1997), which discusses the relevant law in significant depth in Part XIII: Computer Evidence. Additional discussion is contained in the preceding Consultation Paper No CP138 (available at the same link) at paragraphs 14.27–14.32.

In short, the presumption comes from the common law, and in particular Castle v Cross [1984] 1 WLR 1372, 1377B (Stephen Brown LJ). In Castle, the following extract from Phipson on Evidence was approved by the Divisional Court: "In the absence of evidence to the contrary, the courts will presume that mechanical instruments were in order at the material time" — M N Howard, P Crane and D A Hochberg (eds), Phipson on Evidence (14th ed, 1990). The Law Commission felt that this was the appropriate rule.

However, section 69 of the Police and Criminal Evidence Act 1984 (UK) ("PACE Act") had overridden the common law presumption in respect to computers. Under PACE Act s 69, the prosecution had to prove the computer was working properly. The Law Commission recommended repealing that and restoring the common law presumption. Hence, the Youth Justice and Criminal Evidence Act 1999 (UK) eventually repealed PACE Act s 69.

As a response to this reply notes, the repeal has attracted criticism. Christie asserts rather scathingly that "the Law Commission misunderstood, or misrepresented, the opinions of the sources cited as being in favour of repeal", failing to understand the problem and ignoring expert advice: James Christie, "The Law Commission and section 69 of the Police and Criminal Evidence Act 1984" (2023) 20 Digital Evidence and Electronic Law Review.

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    This good answer could be further improved by links to James Christie's series of articles in the Digital Evidence and Electronic Law Review, in particular this recent article revealing that the Law Commission completely misunderstood the evidence that they used to justify the repeal of PACE s.69.
    – Matthew
    Dec 10, 2023 at 21:40
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    – feetwet
    Dec 30, 2023 at 20:38

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