In the case of Gestmin SGPS SA v Credit Suisse (UK) Ltd & Anor  EWHC 3560 (Comm), Mr Justice Leggatt concluded (at paragraph 15 to 22) that witness evidence, based on recalled events that occurred several years in the past (or longer), is limited by the ‘unreliability of human memory’:
While everyone knows that memory is fallible, I do not believe that the legal system has sufficiently absorbed the lessons of a century of psychological research into the nature of memory and the unreliability of eyewitness testimony. One of the most important lessons of such research is that in everyday life we are not aware of the extent to which our own and other people's memories are unreliable and believe our memories to be more faithful than they are. Two common (and related) errors are to suppose: (1) that the stronger and more vivid is our feeling or experience of recollection, the more likely the recollection is to be accurate; and (2) that the more confident another person is in their recollection, the more likely their recollection is to be accurate.
Underlying both these errors is a faulty model of memory as a mental record which is fixed at the time of experience of an event and then fades (more or less slowly) over time. In fact, psychological research has demonstrated that memories are fluid and malleable, being constantly rewritten whenever they are retrieved. This is true even of so-called 'flashbulb' memories, that is memories of experiencing or learning of a particularly shocking or traumatic even ... External information can intrude into a witness's memory, as can his or her own thoughts and beliefs, and both can cause dramatic changes in recollection. Events can come to be recalled as memories which did not happen at all or which happened to someone else ...
Memory is especially unreliable when it comes to recalling past beliefs. Our memories of past beliefs are revised to make them more consistent with our present beliefs. Studies have also shown that memory is particularly vulnerable to interference and alteration when a person is presented with new information or suggestions about an event in circumstances where his or her memory of it is already weak due to the passage of time.
A witness is asked to make a statement, often (as in the present case) when a long time has already elapsed since the relevant events ... The statement is made after the witness's memory has been "refreshed" by reading documents. The documents considered often include statements of case and other argumentative material as well as documents which the witness did not see at the time or which came into existence after the events which he or she is being asked to recall ... The effect of this process is to establish in the mind of the witness the matters recorded in his or her own statement and other written material, whether they be true or false, and to cause the witness's memory of events to be based increasingly on this material and later interpretations of it rather than on the original experience of the events.
In the light of these considerations, the best approach for a judge to adopt in the trial of a commercial case is, in my view, to place little if any reliance at all on witnesses' recollections of what was said in meetings and conversations, and to base factual findings on inferences drawn from the documentary evidence and known or probable facts. This does not mean that oral testimony serves no useful purpose – though its utility is often disproportionate to its length. But its value lies largely, as I see it, in the opportunity which cross-examination affords to subject the documentary record to critical scrutiny and to gauge the personality, motivations and working practices of a witness, rather than in testimony of what the witness recalls of particular conversations and events. Above all, it is important to avoid the fallacy of supposing that, because a witness has confidence in his or her recollection and is honest, evidence based on that recollection provides any reliable guide to the truth’.
Leggatt J’s comments were reiterated in the recent case of The National Union of Mineworkers v Organisation Internationale De L'Energie Et Des Mines  EWHC 1359 (Comm), which was summarised in edition 277 of BC Disease News (here).
Despite not having been cited by counsel in the noise-induced hearing loss (NIHL) case of Mackenzie v Alcoa Manufacturing (GB) Ltd  EWHC 149 (QB), which we analysed in edition 261 (here), the inadequacies of recollected witness evidence can be a significant issue where defendants are unable to produce evidence of noise surveys undertaken several decades in the past – read the judgment of HHJ Inglis in Parkes v Meridian Ltd  EWHC B1 (QB), at paragraphs 133 to 136.
Incidentally, an appeal of the High Court ruling in Mackenzie is expected to be heard in November 2019, where recognition of the ‘fallibility’ of human memory, alongside a declaration that Noise and the Worker (1963) and the Code of Practice (1972) were not intended to have the same binding effect as the Noise At Work Regulations (1989), will be welcomed.
In anticipation of the approaching Mackenzie appeal, it is sensible to scrutinise the Court of Appeal’s recent judgement in Kogan v Martin & Ors  EWCA Civ 1645, in which the lower court’s application of Gestmin to contradictory witness evidence led to the ordering of a re-trial.
At paragraph 88 of his decision, Lord Justice Floyd clarified that:
‘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 ... 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’.
He went on to observe, at paragraph 91, that ‘recourse to the Gestmin ... approach does not justify a selective treatment’.
Full text judgment can be accessed here.