30. Inevitably in such cases, the oral evidence of the key protagonists, most often the mother and her partner, is highly significant. The case law has developed in a way designed to ensure that, whilst there is recognition of the fact that the oral evidence of lay parties is often critical, it also has its limitations; there are dangers in an over reliance by the judge on either demeanour, or upon the fact that a witness has told demonstrable lies.

31. The case of   R v Lucas  [1981] QB 720 is routinely quoted, as it was here at [15] of the judge’s judgment, as a reminder to the court that people lie for all sorts of reasons; the fact that a person lies about one specific thing does not necessarily mean that they have lied about another matter.

32. I have in mind the guidance given by Baker J (as he then was) in   Gloucestershire CC v RH and others   [2012] EWHC 1370 (Fam)  and in particular at [42] his point 7:

“Seventh, the evidence of the parents and any other carers is of the utmost importance. It is essential that the court forms a clear assessment of their credibility and reliability. They must have the fullest opportunity to take part in the hearing and the court is likely to place considerable weight on the evidence and the impression it forms of them (see   Re W and another (Non-accidental injury)  [2003] FCR 346).”

34. In the   Gestmin  case, at [22], Leggatt J expressed the view that the best approach for a judge to adopt in a commercial trial was to place little, if any, reliance on a witness’s recollection of what was said in meetings and conversations; rather factual findings were to be based on inferences drawn from documentary evidence and known or probable facts. This was followed in   Blue v Ashley , where Leggatt J at [70], having rehearsed his own earlier observations in   Gestmin , approached evidence of a crucial conversation in a way that was “mindful of the weaknesses of evidence based on recollection”.

35. The Court of Appeal considered both of these cases in   Kogan v Martin and Others   [2019] EWCA Civ 1645  (‘Kogan’). This was a case where the judge at first instance had wrongly regarded Leggatt J’s statements in Gestmin and Blue v Ashley as an “admonition” against placing any reliance at all on the recollections of witnesses.

36. The Court of Appeal in   Kogan  emphasised the need for a balanced approach to the significance of oral evidence regardless of jurisdiction. Although it was a copyright dispute between former partners, the judgment was a judgment of the court with wider implications.

37. In relation to the treatment of the evidence of the Claimant, the Court in   Kogan  said:

“88…. We start by recalling that the judge read Leggatt J’s statements in   Gestmin v Credit Suisse  and   Blue v Ashley  as an “admonition” against placing any reliance at all on the recollections of witnesses. We consider that to have been a serious error in the present case for a number of reasons. First, as has very recently been noted by HHJ Gore QC in   CBX v North West Anglia NHS Trust  [2019] 7 WLUK 57, Gestmin is not to be taken as laying down any general principle for the assessment of evidence. It is one of a line of distinguished judicial observations that emphasise the fallibility of human memory and the need to assess witness evidence in its proper place alongside contemporaneous documentary evidence and evidence upon which undoubted or probable reliance can be placed. Earlier statements of this kind are discussed by Lord Bingham in his well-known essay   The Judge as Juror: The Judicial Determination of Factual Issues  (from The Business of Judging, Oxford 2000). But a proper awareness of the fallibility of memory does not relieve judges of the task of making findings of fact based upon all of the evidence. Heuristics or mental short cuts are no substitute for this essential judicial function. In particular, where a party’s sworn evidence is disbelieved, the court must say why that is; it cannot simply ignore the evidence.

89. Secondly, the judge in the present case did not remark that the observations in   Gestmin  were expressly addressed to commercial cases. For a paradigm example of such a case, in which a careful examination of the abundant documentation ought to have been at the heart of an inquiry into commercial fraud, see   Simetra Global Assets Ltd & Anor v Ikon Finance Ltd & Ors  [2019] EWCA Civ 1413 and the apposite remarks of Males LJ at paras. 48-49. Here, by contrast, the two parties were private individuals living together for much of the relevant time. That fact made it inherently improbable that details of all their interactions over the creation of the screenplay would be fully recorded in documents. Ms Kogan’s case was that they were bouncing ideas off each other at speed, whereas Mr Martin regarded their interactions as his use of Ms Kogan as a sounding board. Which of these was, objectively, a correct description of their interaction was not likely to be resolved by documents alone, but was a fundamental issue which required to be resolved.

90. Thirdly, having decided to follow the   Gestmin/ Blue  approach, the judge did not apply it to documents which greatly assisted Ms Kogan’s case. The two documents to which the judge referred at [79] strongly supported an inference that the parties were collaborating on the screenplay at the outset, but the judge declined to draw any inference from them, instead observing that this was early in the project and that the affectionate language used gave little idea of how the parties planned to work together on the subsequent drafts. It was, however, important for the judge to come to a conclusion as to the basis on which the original outline was created. He was tasked with deciding, in the words of Keating J, whether Ms Kogan and Mr Martin had “undertaken jointly to write a [screen]play, agreeing in the general outline and design, and sharing the labour of working it out”. Their approach at the outset was highly relevant.”

“72. I do not accept that the mother concocted this evidence. She was thoroughly cross-examined on this evidence and it was clear to me that she was recounting an event that she recalled. She was a truthful witness and I accept her account.”

39. That this evidence went to the heart of the case is demonstrated towards the end of the judgment. The judge, having found that the coffee had been poisoned and having discounted any possible contamination via a water source, said:

“115. The father got up early on the morning of 11 September 2012, something he had not done before when on holiday. The mother had called out that she was staying in bed. He knew the grandparents’ habits. He was behaving in a restless manner hanging around the verandah and when the mother unexpectedly joined him in her pyjamas, he was hovering over the coffee cups and did not respond to her for some seconds.

116. In my judgment, that evidence, taken together with the scientific evidence, is sufficient for me to be satisfied on the balance of probabilities that it was the father who deliberately administered the thallium to the coffee cups.”

40. I do not seek in any way to undermine the importance of oral evidence in family cases, or the long-held view that judges at first instance have a significant advantage over the judges on appeal in having seen and heard the witnesses give evidence and be subjected to cross-examination   (Piglowska v Piglowski  [1999] WL 477307, [1999] 2 FLR 763 at 784). As Baker J said in in   Gloucestershire CC v RH   and others at [42], it is essential that the judge forms a view as to the credibility of each of the witnesses, to which end oral evidence will be of great importance in enabling the court to discover what occurred, and in assessing the reliability of the witness.

41. The court must, however, be mindful of the fallibility of memory and the pressures of giving evidence. The relative significance of oral and contemporaneous evidence will vary from case to case. What is important, as was highlighted in Kogan, is that the court assesses all the evidence in a manner suited to the case before it and does not inappropriately elevate one kind of evidence over another.