The Dekagram: 13th April 2026

This week Megan Bithel-Vaughan issues us with another warning on the use of AI in courts – despite our best efforts, litigators are still being caught out. You can’t say we didn’t warn you! Meanwhile Bethany Hutchison considers whether missing out a line of an address for service is fatal to an application for default judgment.

Another Warning about the Use of AI: Guerin -v- O’Doherty [2026] IECA 48

Another week, another Court of Appeal case warning against the dangers of use of AI, in particular with regards to its tendency to “hallucinate” cases which do not exist. Whilst, as an Irish Court of Appeal case, it is of course not binding on the Courts of England and Wales, nonetheless Guerin -v- O’Doherty sets out both a useful warning and some helpful principles regarding the use of AI by litigants in person.

“Hallucination” is a well-known issue with AI large language models.  As summarised in the September 2025 article Why Language Models Hallucinate, it is characterised by them producing “overconfident, plausible falsehoods, which diminish their utility and trustworthiness” and is believed to occur, “because the[ir] training and evaluation procedures reward guessing over acknowledging uncertainty”.

Despite this well-known issue, AI use is growing across the legal sector, with a wide range of legal research tools now powered by it and the use of large language models also becoming increasingly prevalent. Whilst lawyers are becoming more and more alive to the risk of “hallucination”, worryingly, the use of large language model AI by litigants in person, as opposed to those technologies specifically tailored to legal research, is growing significantly.

I do not intend to set out the specific factual circumstances of Guerin -v- O’Doherty, nor the legal arguments contained therein, as they relate to Irish law. In brief, this is a defamation case in which the defendant had begun the proceedings legally represented, but become a litigant in person midway through. The defendant, as a litigant in person, was appealing against a decision not to strike out the plaintiff’s defamation claim.

The relevant portion of the judgment for our purposes begins at paragraph 72. Ms Justice Costello identifies that the defendant had prepared the written submissions in support of her appeal using an AI large language model and her written submissions had included several references to authorities which had been “hallucinated”.

As Ms Justice Costello notes,

“This is an inherent and well-known risk of using AI to write legal submissions. The defendant did not apparently verify the existence of the authorities she cited, or that the cases relied upon actually supported the propositions advanced. Neither did she notify the solicitors for the plaintiff that she had prepared her submissions with the assistance of AI.”

Ms Justice Costello reinforces that being a litigant in person is not an excuse to mislead the Court with authorities that do not exist, nor should a different standard be applied to them. This is in effect, a restatement of the principle in Barton v Wright Hassall [2018] UKSC 12, that a litigant in person is just as bound by their obligations to the Court (in the case of Barton, their obligations under the Civil Procedure Rules), as a legally represented party. All parties, both legally represented and not, have a duty not to mislead the Court and, whether advertently or otherwise, must not advance propositions on the basis of a fake authority.

Ms Justice Costello sets out the following principles for litigants in person who are using AI:

• Whilst parties are entitled to use AI as an assistive measure, any use of AI must be used responsibly and measures taken to verify the cases cited to ensure that they properly exist.
• No case should be cited without the party who is relying on it actively verifying that it is a genuine judgment of the Court and arguably supports the propositions advanced using it.
• Where AI is used, the other parties should be expressly informed of their use in this regard.
• A litigant in person is just as responsible for their written or oral submissions as legal representatives are.

Further, this case highlights how irresponsible use of AI significantly adds to the costs of the other side preparing their response to any application / claim, as there is significant wasted time in searching for authorities which do not exist. This reminds us that parties, including litigants in person, should be aware of the risk of wasted costs orders being made against them should irresponsible AI usage cause fake cases to be cited before the Court.

About the Author

Megan Bithel-Vaughan gained tenancy having completed pupillage at Deka Chambers. She has already been led by Sarah Prager KC in a case of significant value involving complex issues around the interpretation of the Montreal Convention, and in particular the interplay between the operation of the partial compensation cap and contributory negligence.

Service, Addresses, and the Limits of Technical Challenges: Eco Green Capital v Wetzel [2026] EWHC 800 (KB)

There is a particular type of procedural argument that can be very tempting to defendants faced with default judgment. It usually runs something like this: “the address was not quite right, therefore service was invalid,, and therefore everything falls away. Oh and by the way, I’ve never seen this claim form before in my life”. Mr Justice Turner’s decision in Eco Green Capital Ltd v Wetzel [2026] EWHC 800 (KB)is a clear and practical reminder that this kind of argument will likely only succeed where there has, in fact, been a defect, and that defect has had a prejudicial impact.

The facts of the case are background only to the issues considered in this judgment; but the case arose out of a default judgment for over £80,000 awarded in favour of a company specialising in the installation of renewable heating systems. The defendant sought to set the default judgment aside, arguing that the claim form had not been properly served.

The argument centred on a small but, it was said, critical omission. The claim form included the defendant’s house name, village, and postcode, but did not include the street name “Heads Lane”, which appeared on the Land Registry title. The submission was straightforward: the address was incomplete, therefore it did not comply with CPR 6.6, and service was invalid. There was also an argument that the Defendant had not, in fact, received the claim form due to this omission.

The Defendant’s submission did not get very far, with Mr Justice Turner undertaking a pragmatic review of the civil procedure rules on service.

CPR 6.6(2) provides:

“Where to serve the claim form – general provisions

6.6…

(2) The claimant must include in the claim form an address at which the defendant may be served. That address must include a full postcode, unless the court orders otherwise.”

CPR PD 16 provides, in so far as is material:

“The claim form

2.1 The claim form must include an address (including the postcode) at which the claimant lives or carries on business, even if the claimant’s address for service is the business address of their solicitor.

2.2 Where the defendant is an individual, the claimant should (if able to do so) include in the claim form an address (including the postcode) at which the defendant lives or carries on business, even if the defendant’s solicitors have agreed to accept service on the defendant’s behalf.

2.3 If the claim form does not include a full address, including postcode, for all parties the claim form will be issued but retained by the court and not served until the claimant has supplied a full address, including postcode, or the court has dispensed with the requirement to do so. The court will notify the claimant.”

CPR 6.9 provides that where, as here, the defendant does not give an address at which the defendant may be served then, in the case of an individual, the place of service is his or her usual or last known residence.

Mr Justice Turner considered that the key question is not whether the address is a perfect match for every official record. The real question is whether the address provides a clear and unique identification of the defendant’s residence. In this case, it plainly did. The postcode covered only a handful of properties. All were located on Heads Lane. Each property was identified by name, not number. Including “Heads Lane” in the address would not have made the property any easier to identify, nor reduced any real risk of confusion. In other words, the omission was immaterial.

The judge was explicit that the rules are not intended to introduce an unnecessary layer of technicality that could undermine the overriding objective. If even minor deviations were treated as fatal, regardless of their having no practical impact, perfectly valid claims could be entirely derailed on a technicality.

The judgment provides a useful clarification of how CPR 6.6 should be applied in practice:

• the postcode is mandatory;
• other elements of the address are contextual and fact dependent;
• the aim is to ensure the defendant can be identified and located in reality, not in theory. This is particularly important in rural settings, where properties may not have street numbers, or where house names are the primary identifier.

Having found that the address was sufficient, the court went on to consider the evidence as to whether or not the claim form had, in fact, been delivered to the Defendant’s home:

• there had been multiple pieces of correspondence sent to the same address, none of which had been returned, and several of which had actually been signed for by the Defendant;
• the Defendant herself had used the same address in contractual documents;
• upon enforcement action being taken following default judgment, enforcement officers had no difficulty locating the property; and,
• the enforcement officers and an accompanying police officer who visited the Defendant’s address recorded on their body-worn cameras ‘piles of paper and unopened envelopes head up in the kitchen’. The Defendant conceded only that there was ‘some unopened post lying on my table and in my postbox and I admit that there was a few letters that I had not collected’. The court was not convinced.

The lesson for defendants is clear: if the postman can find you, so can the court, and ignoring the mail won’t save you from the contents therein. For claimants, it’s a reassuring tale; when service has, in fact, been effective and no response to a claim has been received, the technicality of a missed address line will not thwart a validly entered default judgment.

About the Author

Bethany Hutchison was called in 2021. Prior to joining chambers she gained a broad range of experience working in the legal advisory teams in the Cabinet Office and the Ministry of Housing, Communities and Local Government, following successful completion of her pupillage with the Government Legal Department, advising on high profile commercial, immigration and contractual matters during that time. She is now developing a busy common law practice across the full range of chambers’ specialisms.