BCS Law specialist group

Watch the video



The Post Office Horizon scandal has been a legal catastrophe, both civil and criminal. It is predicated on the legal presumption that computers are reliable. In this session the speakers will consider why the presumption came into being, where it came from and why it is wrong.

The speakers will also consider the consequences of the presumption in practice: where the problems lie and why, especially in relation to legal aid and widespread ignorance of electronic evidence within the legal profession.

The session will also briefly consider ‘AI’ and ‘algorithmic decision making’. The question is whether it is or is not a panacea and whether it will cause even greater problems.

AI might not be a panacea and may be a Pandora’s jar. Finally, the speakers will consider some problems with AI - indeterminate and unpredictable output not capable of replication, and the ramifications of AI in legal proceedings: that is, untestability.

About the speakers

Paul Marshall is a commercial barrister at Cornerstone Barristers, 2-3 Gray’s Inn Square, London, He is ranked in Chambers & Partners’ global rankings. Illness afforded him the opportunity to volunteer, without payment, to represent some of those wrongfully prosecuted by the Post Office in their criminal appeals to the Court of Appeal. With his junior, Flora Page, Paul was alone in contending that “category two abuse of process” (essentially, conduct undermining the integrity of the criminal justice system) should be determined by the Court of Appeal as a separate ground of appeal, contrary to the view of all the other criminal QCs and lawyers involved in the appeals. The Court of Appeal agreed to hear that as separate ground of appeal (rejecting the Post Offices objections), and upheld it. That finding opens the way to potential further claims against the Post Office for malicious prosecution. He was responsible for eliciting from the Post Office in November 2020 the “Clarke Advice” that revealed that the Post Office knew of serious errors in its Horizon computer system and of misleading evidence, that the Post Office had given to the court, as long ago as 2013.

Stephen Mason is editor, with Professor Daniel Seng, of Electronic Evidence and Electronic Signatures (5th edn, Institute of Advanced Legal Studies for the SAS Humanities Digital Library, School of Advanced Study, University of London, 2021). Please see: https://humanities-digital-library.org/index.php/hdl/catalog/book/electronic-evidence-and-electronic-signatures for free access to that publication.

Flora Page is a criminal barrister at 23ES Chambers and a PhD candidate at UCL. She prosecutes at the highest CPS grade for junior counsel, but her practice is 50% defence. She volunteered to assist the team led by Paul Marshall in the Post Office appeals. She has been in criminal practice since 1999, and has also worked at the Law Commission, the Financial Conduct Authority and the University of Law.

Harold Thimbleby, Professor and See Change Digital Health Fellow, Swansea University, Wales, and Visiting Professor, UCL, London, Emeritus Professor, Gresham College, London is an internationally-recognised computer scientist who has spent his career trying to improve the quality (primarily the safety and usability) of computer systems. He has been an expert witness in several NHS court cases and investigations involving unreliable computer systems that have led to patient harms and, in some cases, to death. His latest book, ‘Fix IT How to see and solve the problems of digital healthcare’ is published by Oxford University Press, 2021.

Martyn Thomas CBE, Emeritus Professor, Gresham College, London and Visiting Professor of Software Engineering at Aberystwyth University, Wales is a software engineer specialising in safety-critical systems and cyber-security.

Our events are for adults aged 16 years and over.

For overseas delegates who wish to attend the event, please note that BCS does not issue invitation letters.

This event is brought to you by: BCS Law specialist group

Webinar: Computers - the enduring error: output = truth
Date and time
Tuesday 21 September, 6:30pm - 7:35pm
This event is sold out