The Dekagram: 13th July 2026

This week Anirudh Mandagere has written a longer briefing on the use by lawyers of artificial intelligence and how to avoid being accused of negligence (it’s not as straightforward as you may think); the link to his briefing is here. Meanwhile Sarah Prager KC draws attention to yet another case involving unsatisfactory expert evidence.

In other (related) news, the Technology and Construction Court Guide was published last week, and the guidance provided for the use of artificial intelligence is likely to be indicative of the general direction of travel of the higher courts in this regard. The Guide acknowledges that AI can be employed, but stresses that litigators who choose to use it continue to bear responsibility for its output and should, if in doubt, disclose that it has been used. Section 1.6 of the Guide states in full:

1.6.1 All legal representatives are personally responsible for the material they put before the Court and have a professional obligation to ensure that it is accurate and appropriate. Provided that representative are mindful of that responsibility and of their professional obligations, Artificial Intelligence (“AI”) can be used.

1.6.2 Whether and to what extent legal representatives should disclose their use of AI will depend on the context. However, any doubt as to whether the fact that AI has been used should be mentioned must be resolved in favour of disclosing such use.

1.6.3 Legal representatives must at all times uphold the confidentiality of and protect the privacy of any underlying data in relation to which Artificial Intelligence is used.

1.6.4 Legal representatives must independently verify the accuracy of any research or case citations that have been generated with the assistance of AI and must be in a position to confirm that they have done so.

1.6.5 Further guidance on the use of Artificial Intelligence may be obtained from Artificial Intelligence (AI); Guidance for Judicial Officer Holders dated 31 October 2025 at https://www.judiciary.uk/guidance-and resources/artificial-intelligence-ai-judicial-guidance-october-2025/.

Experts on Trial: another judgment focussing on expert evidence

We have commented before in the Dekagram on the increasing willingness of judges to criticise expert witnesses more harshly than was historically considered appropriate. This week saw a further judgments to add to the growing corpus.

In Nord Stream AG v Lloyd’s Insurance Company S.A. & others [2026] EWHC 1685 (Comm) Dame Clare Moulder DBE, sitting as a High Court Judge in the Commercial Court, was concerned with a dispute between the owner of two natural gas pipelines and its insurer (you may have read in the press about the extraordinary events giving rise to the claim). The trial took place over 6 weeks and included expert evidence in the following disciplines:

• Geopolitics;
• Energy insurance market practice;
• Materials Science and Explosives Science;
• Subsea operations;
• Quantum of repair.

All much more exciting and highbrow than this humble author’s daily fayre.

As regards the geopolitical expert evidence, the court held, at [37] that:

“Whilst I do not doubt his qualifications, in my view the evidence of Dr Less was unsatisfactory in that he appeared at times to be seeking to support the Claimant’s case by advancing arguments that in my view flew in the face of common sense and the inferences to be drawn from the known facts.”

A by now familiar criticism, and one that is inexcusable; experts and those instructing them should be well aware that they should be providing opinion evidence and not advocacy services.

Similarly, the pipeline engineer instructed by the claimant failed to impress the court favourably. At [64]:

“in cross examination there were occasions where Mr Lumley in my view gave answers which appeared to be speculative with no evidential basis and when considered cumulatively, I am left with the impression that Mr Lumley was seeking to defend the Claimant’s position by speculation where necessary. For example, Mr Lumley was asked in cross examination about an anchor drag as a possible explanation of the Dent, initially resisting the proposition that an anchor drag would cause a visible disturbance to the seabed suggesting a “bouncing anchor”. It is unclear how even a bouncing anchor would not cause a visible disturbance and Mr Lumley ultimately accepted that there was no scar and anchor drag was not a “credible cause”.”

Furthermore, he had not made it clear in his written reports that he had relied on modelling undertaken by others; the court took a dim view of his failure to make clear the bounds of his expertise. The court concluded that:

“In light of the matters referred to above, I therefore do not propose to give weight to Mr Lumley’s views on the mechanics of an explosion as I cannot be satisfied that it is reliable or comprehensive.”

In summary, some of the experts instructed by the claimant went too far in seeking to assist, not the court, but the party by whom they were instructed. It is high time, in the view of the author, that litigants learned the lessons of CPR Part 35 and of the ever-lengthening line of authority to the effect that experts who take on the mantle of advocates never prosper – and nor do their clients.

About the Author

Called to the Bar in 1997, Sarah Prager KC has been listed in the legal directories in travel and personal injury law for many years, and, more recently, listed in aviation as well. Together with Matthew Chapman KC, Jack Harding, Dominique Smith and Tom Yarrow, she co-writes the leading legal textbook in the area, and has been involved in most of the leading cases in the field in the last few decades. She undertakes purely domestic high value personal injury work as well as cross border work and has a wealth of experience of difficult and sensitive cases, including serious sexual assault and cases involving children.