Post Office Horizon IT scandal

Notes by Stephen Mason, April 2025

 

The Post Office Horizon IT scandal is the worst in British history, although England & Wales is the most shameless.

It is caused by a number of factors, including the presumption that computers are reliable (whatever reliable means, for which see the articles below).

If this presumption did not exist, the Post Office and other prosecutors might not have succeeded in the nefarious way they did.

I am the only lawyer that has considered this in detail and have done so since the second edition of Electronic Evidence in 2010.

The fact is, the main legal problem that the subpostmasters and subpostmistresses faced is the failure of lawyers (both solicitors and barristers) to understand electronic evidence and the failure of judges to order disclosure of relevant evidence (the case of Seema Misra illustrates this, for which see the transcript of her trial below and the practitioner textbook for judges and lawyers, also below).

Precis of the issues

These two short articles set out the issues concisely:

Stephen Mason, ‘The presumption that computers are reliable’, Counsel, July 2024, 34-6, https://www.counselmagazine.co.uk/articles/the-presumption-that-computers-are-reliable (in this article I explain the 2 ways of approaching the presumption that computers are reliable)

Stephen Mason, ‘The cause of the Post Office Horizon scandal? The Law Commission? Judges? Lawyers?’ Computer Weekly, 1 November 2023, online

https://www.computerweekly.com/opinion/The-cause-of-the-Post-Office-Horizon-scandal-The-Law-Commission-Judges-Lawyers

The Briefing Note below was written for Members of Parliament:

Nicholas Bohm, James Christie, Peter Bernard Ladkin, Bev Littlewood, Paul Marshall, Stephen Mason, Martin Newby, Steven J. Murdoch, Harold Thimbleby and Martyn Thomas CBE, ‘Briefing Note: The legal rule that computers are presumed to be operating correctly – unforeseen and unjust consequences’, 19 Digital Evidence and Electronic Signature Law Review (2022) 123 – 127

https://journals.sas.ac.uk/deeslr/article/view/5476

Stephen Mason, ‘The UK Post Office Horizon IT scandal: Part 1: an outline of the chronology’, (2024) 30 Computer and Telecommunications Law Review, Issue 3, 59-63

Stephen Mason, ‘The UK Post Office Horizon IT scandal, Part 2: the legal issues’, (2024) 30 Computer and Telecommunications Law Review, Issue 4, 96-101

The presumption that computers are reliable

For a full treatment of this presumption, demonstrating the fact that software is not reliable, see chapter 5 of the open-source practitioner text for judges, lawyers and legal academics: Stephen Mason and Daniel Seng, editors, Electronic Evidence and Electronic Signatures (5th edition, Institute of Advanced Legal Studies for the SAS Humanities Digital Library, School of Advanced Study, University of London, 2021)

https://uolpress.co.uk/book/electronic-evidence-and-electronic-signatures/

For a devastating and damming review of the Law Commission’s arguments leading to the recommendation that computers should be presumed to be reliable, see:

James Christie, The Law Commission and section 69 of the Police and Criminal Evidence Act 1984, 20 Digital Evidence and Electronic Signature Law Review (2023) 62 – 95

https://journals.sas.ac.uk/deeslr/article/view/5642

The Post Office (31 July 1995), Inland Revenue (16 October 1995), BT (27 October 1995), CPS (1 November 1995) and DTI (9 November 1995) wrote to the Law Commission supporting the presumption that computers are reliable. I published each of their responses in 2023:

https://journals.sas.ac.uk/deeslr/article/view/5649

2010 Seema Misra

When I became aware of Seema Misra’s case, I contacted her lawyer (Issy Hogg) to offer help and point out our book. I was not asked to help (although I offered my help for free). I obtained the permission of the judge to buy and publish the transcript of her trial in the journal I founded (Seema Misra also agreed to publication), which indirectly helped the scandal increase pace against the Post Office

https://journals.sas.ac.uk/deeslr/issue/view/328

Tim McCormack, ‘The Post Office Horizon system and Seema Misra’ 13 Digital Evidence and Electronic Signature Law Review (2016) 133-138

https://journals.sas.ac.uk/deeslr/article/view/2303

Court of Appeal misunderstanding of software

Peter Bernard Ladkin, Stephen Mason and Harold Thimbleby ‘Misunderstanding Digital-Computer Technology in Court: A Commentary’, 21 Digital Evidence and Electronic Signature Law Review (2024), 1-13

https://journals.sas.ac.uk/deeslr/article/view/5776/5406

Articles dealing with how a legal system can approach evidence in electronic form – the articles below refer to all legal proceedings in any jurisdiction – they are not limited to England & Wales

Michael Jackson, ‘An approach to the judicial evaluation of evidence from computers and computer systems’ 18 Digital Evidence and Electronic Signature Law Review (2021) 50-55

https://journals.sas.ac.uk/deeslr/article/view/5289

The article below is a slightly revised version of a report submitted to the Ministry of Justice in response to the invitation by Mr Alex Chalk MP, then Parliamentary Under-Secretary of State (now Solicitor General), to Paul Marshall, Barrister, in August 2020 to prepare a paper on proposed recommendations for improving the existing approach under rules of court for the disclosure in court proceedings of computer-derived evidence. The paper was submitted to the Ministry of Justice in November 2020. The paper is understood to have been referred by the Under-Secretary of State to the Attorney General and the Chair of the Criminal Procedure Rule Committee for their consideration. No action has been taken.

Paul Marshall, James Christie, Peter Bernard Ladkin, Bev Littlewood, Stephen Mason, Martin Newby, Jonathan Rogers, Harold Thimbleby, Martyn Thomas CBE, ‘Recommendations for the probity of computer evidence’, 18 Digital Evidence and Electronic Signature Law Review (2021) 18-26

https://journals.sas.ac.uk/deeslr/article/view/5240

Articles dealing with the ‘reliability’ of computers

James Christie, ‘The Post Office Horizon IT scandal and the presumption of the dependability of computer evidence’, 17 Digital Evidence and Electronic Signature Law Review (2020) 49-70

https://journals.sas.ac.uk/deeslr/article/view/5226

Peter Bernard Ladkin, ‘Robustness of software’ 17 Digital Evidence and Electronic Signature Law Review (2020) 15-24

https://journals.sas.ac.uk/deeslr/article/view/5171

Peter Bernard Ladkin, Bev Littlewood, Harold Thimbleby and Martyn Thomas CBE, ‘The Law Commission presumption concerning the dependability of computer evidence’, 17 Digital Evidence and Electronic Signature Law Review (2020) 1-14

https://journals.sas.ac.uk/deeslr/article/view/5143

Articles dealing with the consequences when relying on the ‘reliability’ of computers

James Christie, ‘The Post Office IT scandal – why IT audit is essential for effective corporate governance’, 19 Digital Evidence and Electronic Signature Law Review (2022), 42-86

https://journals.sas.ac.uk/deeslr/article/view/5425

Paul Marshall, ‘Scandal at the Post Office: The Intersection of law, ethics and politics’, 19 Digital Evidence and Electronic Signature Law Review (2022), 12-28

https://journals.sas.ac.uk/deeslr/article/view/5395

Paul Marshall, ‘The harm that judges do – misunderstanding computer evidence: Mr Castleton’s story, 17 Digital Evidence and Electronic Signature Law Review (2020) 25-48

https://journals.sas.ac.uk/deeslr/article/view/5172

Miscarriage of justice and legal advice

Richard Moorhead, Karen Nokes and Rebecca Helm. Independent Review, ‘Miscarriages of Justice, and Computer Evidence: Brian Altman KC’s General Review and the Post Office Scandal’, 20 Digital Evidence and Electronic Signature Law Review (2023) 96-19

https://journals.sas.ac.uk/deeslr/article/view/5643

Below is a list of calls for the education of student lawyers, lawyers and judges, all of which have been ignored:

Editorial, 4 Digital Evidence and Electronic Signature Law Review 2007

Editorial, 7 Digital Evidence and Electronic Signature Law Review 2010

Editorial, 9 Digital Evidence and Electronic Signature Law Review 2012 – particularly pertinent

Editorial, 10 Digital Evidence and Electronic Signature Law Review 2013 [PLUS a FREE syllabus, https://journals.sas.ac.uk/deeslr/article/view/2017]

I commissioned the following two articles by Denise Wong and Deveral Capps. Neither were certain that the teaching of electronic evidence was necessary before they gave the topic any thought, but both agreed it was after writing their papers. Two elegant essays:

Denise H Wong, ‘Educating for the future: teaching evidence in the technological age’ 10 Digital Evidence and Electronic Signature Law Review (2013) 16-24

https://journals.sas.ac.uk/deeslr/article/view/2018

Deveral Capps, ‘Fitting a quart into a pint pot: the legal curriculum and meeting the requirements of practice’ (2013) 10 Digital Evidence and Electronic Signature Law Review (2013) 23-28

https://journals.sas.ac.uk/deeslr/article/view/2019

Editorial, 13 Digital Evidence and Electronic Signature Law Review 2016

Editorial, 17 Digital Evidence and Electronic Signature Law Review 2020