A example of the thinking process used in granting permission to call expert evidence for a very high profile trial.

Warby J said,

19 The first question to address on any application to call expert evidence must be whether the evidence is admissible. [The judge cited Section 3 of the Civil Evidence Act 1972 and the case of Barings Plc (see specific posts)]…

21 There was no contest between the parties on whether these requirements were met in relation to the two proposed experts, but it remains a matter for the court to decide. I had no difficulty in concluding that phonetics is a recognised academic discipline which encompasses the scientific study of rates of speech, and is governed by recognised standards of conduct. It is sufficiently clear that the chosen witnesses each possess sufficient knowledge to enable them to provide evidence of speech rates applicable to this case which has potential value to the trial judge. The issue to which such evidence would go is on any view the main issue in both actions. The account of the evidence that would be given satisfied me that it was capable of influencing the court’s decision on that issue.

22 [The judge returned to Barings Plc]…

23 The court must also have regard to CPR 35.1 which provides that “Expert evidence shall be restricted to that which is reasonably required to resolve the proceedings.”

24 Here, the trial judge could arrive at a decision on the central issue in these cases without reference to expert or any analysis of speech rates, but instead by assessing the witnesses, their credibility, and the probabilities in the light of all the other evidence including the CCTV. It is naturally a matter for concern that the position adopted on one side of the issue is that evidence of this kind, if adduced, will be inconclusive. In that event, the evidence would not have been helpful but its admission would have been wasteful. It does not follow, however, nor could I take the view, that this evidence will not be helpful in resolving the issue justly.

25 The case for Mr Mitchell, as explained by his Leading Counsel, is that the evidence would not only be helpful but it would be conclusive in his favour. I was in no position to dismiss that as a real possibility. Where a party to civil litigation credibly alleges that expert evidence he has obtained will show that his opponent’s case cannot be true, that must be a powerful factor in favour of permitting the evidence to be led. It also seemed to me that there is a real prospect that, if not conclusive, objective evidence of this kind would help the trial judge reach a conclusion as to the probabilities on the central issue. The evidence is potentially of value, perhaps very great value, in resolving the issues.

26 The case for admitting the evidence is bolstered by the fact that these cases have an important public dimension and have attracted considerable public attention. It is highly desirable that their outcome should be one that commands public confidence. The process should not be vulnerable to the charge that one or the other party has been unreasonably denied an opportunity to lead evidence which, had it only been heard, would have altered the outcome.

27 CPR 35.1 imposes a duty on the court to restrict expert evidence to that which is reasonably required. I do not, however, read this as imposing a test of absolute necessity. A judgment has to be made in the individual case, and it has to be made before the evidence is heard and evaluated. My conclusion was that evidence which it is credibly said could conclusively determine the single most important issue in the case meets the criterion in the rule.

28 For those reasons I granted permission to each party to lead expert evidence on the issue identified above…

29 The second topic identified at the CMC as a potential area for expert evidence was “field of vision/trajectory analysis”. The issue on which Mr Mitchell and then the other parties all sought permission to call expert evidence when they issued their application notices was “the number of members of the public it was possible for Toby Rowland to have had in his field of vision before the point at which he claims he gave Andrew Mitchell MP a verbal warning pursuant to the Public Order Act 1986 .”

41 …I nonetheless decided to grant permission to both parties, for these reasons.

42 Taking Mr Mitchell’s application first, the expertise of Prof [W] was apparent from his CV. I was satisfied that optometry and in particular peripheral vision are recognised fields of expertise, in relation to which Prof [W]is a qualified expert…I saw no reason to doubt that Prof [W] is able to perform that task. Mr Mitchell says that he can through this evidence demonstrate not just that PC Rowland probably did not but that PC Rowland cannot have seen visibly shocked members of the public before giving the warning. I could not at this stage reject that proposition, advanced through Leading Counsel. Even if the evidence falls short of proving impossibility there is a real prospect it will assist in resolving the probabilities. It appears to be evidence that is potentially of value in resolving this important issue. It is reasonably required for reasons similar to those identified above in respect of the phonetics evidence. It can be served in a short space of time, with sufficient time before trial.

43 …Mr [P] appeared to me to possess considerable expertise, recognised by courts on a number of occasions, in reconstructing events with precision. He was in my judgment sufficiently qualified within the meaning of s 3 of the Civil Evidence Act 1972 to provide the court with opinion evidence, by means of a report and 3D computer graphics, on the issue of what PC Rowland could have seen. I found that his evidence would be potentially helpful in resolving whether PC Rowland could have seen members of the public and if so where and when. If his evidence was excluded the court would be left with no cross-check on Prof [W]’s conclusions. I concluded that any risk of unfairness to Mr Mitchell could be adequately catered for by the court making due allowance in assessing the weight to give to Mr [P]’s conclusions, to the extent they differ from those of Prof [W].

Edited for ease of reading. See other cases cited under this tag.