" 3.6 Trial witness statements should not – … (4) include commentary on other evidence in the case (either documents or the evidence of other witnesses)…"
"If a party fails to comply with any part of this Practice Direction, the court may, upon application by any other party or of its own motion, do one or more of the following – (1) refuse to give or withdraw permission to rely on, or strike out, part or all of a trial witness statement…"
" 39. Mr Goldberger would not be allowed at trial to give oral evidence which merely recites the relevant events, of which he does not have direct knowledge, by reference to documents he has read. Nor would he be permitted at trial to advance arguments and make submissions which might be expected of an advocate rather than a witness of fact. These points are made clear in paragraph 7 of Appendix 9 to the Chancery Guide 7th ed (2013)… 40 Nor would Mr Goldberger be permitted to give expert opinion evidence at the trial. A witness of fact may sometimes be able to give opinion evidence as part of his or her account of admissible factual evidence in order to provide a full and coherent explanation and account…..Mr Goldberger, however, has expressed his opinions on market practice by way of commentary on facts of which he has no direct knowledge and in which he cannot give direct evidence. In that respect he is purporting to act exactly like an expert witness giving opinion evidence. Permission for such expert evidence has, however, been expressly refused. 41 I recognise, of course, that these rules as to witness statements and their contents are not rigid statutes. It is conceivable that in particular circumstances they may properly be relaxed in order to achieve the overriding objective inCPR r 1 of dealing with cases justly. I can see no good reason, however, why they should not apply to Mr Goldberger's witness statement in the present proceedings."
"(1) subject to any rules of court made in pursuance of… this Act, where a person is called as a witness in any civil proceedings, his opinion on any relevant matter on which he is qualified to give expert evidence shall be admissible in evidence. (2) It is hereby declared that where a person is called as a witness in any civil proceedings, a statement of opinion by him on any relevant matter on which he is not qualified to give expert evidence, if made as a way of conveying relevant facts personally perceived by him, is admissible as evidence of what he perceived ."
" As a matter of practice in the TCC, technical and expert opinions are frequently expressed by factual witnesses in the course of their narrative evidence without objection being taken. Such opinion evidence does not have the same standing as the evidence of independent experts… However such evidence is usually valuable and it often leads to considerable saving of costs ": and at [672] "
" The next task is to quantify the loss. Where that involves a hypothetical exercise, the court does not apply the same balance of probability approach as it would to the proof of past facts. Rather it estimates the loss by making the best attempt it can to evaluate the chances, great or small… taking all significant factors into account."