In Siemens Mobility Ltd v High Speed Two (HS2) Ltd [2022] EWHC 2190 (TCC) Mrs Justice O’Farrell considered an argument that the technical issues that arose in an action led to the need for experts to attend court. This argument was not accepted.  If the legal representatives required technical assistance they could obtain this. There was no need for experts to give formal reports or attend trial.

“it is open to the parties to engage the assistance of experts, even where such experts do not give written or oral testimony for the purposes of the trial.”


The claimant had issued a challenge following a procurement exercise relating to the provision of rolling stock units for the HS2 railway.  The claimant argued that expert evidence was needed because the technical background was so complex expert evidence would  allow the court to reach a proper view on the issues in dispute.  It was also argued that the lawyers involved needed the input of experts to enable them to come to grip with the technical issues.


The judge considered the applicable test for allowing a party to rely on expert evidence.
The applicable test
    1. The principles applicable to any application by a party to rely on expert evidence are not in dispute.
    1. CPR 35.1 provides that:
“Expert evidence shall be restricted to that which is reasonably
required to resolve the proceedings.”
    1. Although the court’s permission is not generally required to instruct an expert, the court’s permission is required before an expert’s report can be relied upon or an expert can be called to give oral evidence (CPR 35.4).
    1. Experts may provide evidence on any matter relevant to the issues to be decided by the court on which the expert is qualified to give expert evidence, including an issue in the proceedings, although they may not usurp the role of the court in determining such issues: Civil Evidence Act 1972 s.3(3); Liddell v Middleton [1996] PIQR (CA) per Stuart-Smith LJ at p.43:
“We do not have trial by expert in this country; we have trial by judge.”
    1. In R. (AB) v Chief Constable of Hampshire Constabulary [2019] EWHC 3461 (Divisional Court) at [117], Dame Victoria Sharp, PQBD made the following observations as to the value of expert evidence in claims for judicial review:
“… it follows from the very nature of a claim for judicial review that expert evidence is rarely reasonably required in order to resolve such a claim … While there will be some occasions when expert evidence is needed on some technical issue, the views of experts on whether or not a decision is rational or otherwise lawful in public law terms will not be admissible. See generally the observations of the Divisional Court in R (Law Society) v Lord Chancellor [2018] EWHC 2090 (Admin) at para 36.”
    1. In the context of procurement claims, the circumstances in which expert evidence will be permitted was considered by Coulson J (as he then was) in By Development Limited v Covent Garden Market Authority [2012] EWHC 2456 (TCC):
“[20] In summary, I consider that the authorities demonstrate that, where the issues are concerned with manifest error or unfairness, expert evidence will not generally be admissible or relevant in judicial review or procurement cases. That is in part because the court is carrying out a limited review of the decision reached by the relevant public body and is not substituting its own view for that previously reached; in part because the public body is likely either to be made up of experts or will have taken expert advice itself in reaching the decision; and in part because such evidence may usurp the court’s function.
[21] All of that said, however, I believe that it goes too far to say that expert evidence can never be admissible in public procurement cases concerned with manifest error. In some cases, it may be required by way of technical explanatory evidence (Lynch). In addition, there may be other cases where, unusually, such evidence is both relevant and necessary to allow the court to reach a conclusion on manifest error. That may be particularly so where the particular issue is specific and discrete, such as a debate about one of the criteria used in the evaluation (Henry Bros) or complex issues of causation (Harmon). Thus, I do not accept the submission, trailed at one point in Mr Giffin’s skeleton argument, that, if expert evidence is required to support an allegation of manifest error, that would of itself indicate that the error could not be manifest. In my view, that would always depend on the facts of the particular case.
[22] Having concluded that expert evidence is not generally admissible in a case of this type, but that there may be unusual circumstances which justify the use of experts, I turn to the particular facts of this case. Is this a claim where the technical background is so complex that explanatory expert evidence is required, and/or is this an unusual case where expert evidence on some or all aspects of the tender evaluation process is required in order to allow the court to reach a proper view on the issues of manifest error or unfairness?”
    1. In the circumstances of this case, the material principles that apply are as follows:
i) A party seeking to adduce expert evidence must identify the particular issues on which it considers that technical explanation may be needed, the nature and scope of the expert evidence that it wishes to rely on, and explain why it is needed to resolve the dispute.
ii) Where the issue for the court is compliance with procurement regulations, based on a review of the process and the decision, as opposed to the merits of the technical solution which is the subject of the procurement, in most cases it is unlikely that expert evidence will be necessary to determine the claim.
iii) Expert evidence may be permitted where the court is satisfied that it is necessary to explain technical issues that are not capable of agreement between the parties, and not evident from the factual witnesses and documentary evidence before the court.
iv) Expert evidence may be permitted where it is necessary to allow the court to reach a conclusion on manifest error, where the technical issues are particularly complex.
v) Expert evidence is not appropriate where that would have the effect of the experts descending into the arena and giving opinions on the matters in issue between the parties, as that would usurp the court’s proper function.


The judge went through each of the arguments raised by the claimant in support of the application that expert evidence be adduced.

  • The claimant had failed to provide any list of expert issues prior to issuing the application.
  • The issues that had now been identified were not relevant to the pleaded case.

The judge found that in each of the five aspects that the claimant sought to adduce evidence there was no need for such evidence, in some cases the pleadings failed to identify any issue on which expert evidence is required.


The judge considered the argument that the legal representatives required technical assistance.  She stated that experts could be retained by parties to assist in litigation even when those experts were not giving evidence. It was possible that such experts would be allowed to have some access to the documents subject to a confidentiality ring. This was an issue that would have to be determined at a later date.


    1. Ms McCredie raised concerns about the ability of the legal team to understand the documents disclosed into Tier 1 of the Confidentiality Ring without expert input.
    1. As set out above, it is open to the parties to engage the assistance of experts, even where such experts do not give written or oral testimony for the purposes of the trial. Although Siemens will have its own in-house technical expertise, the issue is whether Siemens, or other technical experts, should have access to documents within the Confidentiality Ring.
  1. That is a separate question from the matter before the court on this application. During the course of their submissions, the parties indicated that it was likely that some measure of agreement could be reached to extend Siemens’ access to the Tier 1 documentation. Any matter that is not capable of agreement will be considered by the court at the next hearing.