Expert evidence: Essential expert advice

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Expert evidence can be a crucial part of the litigation process. The success or failure of a party’s case can hinge upon what an expert says, or how the expert performs at trial.  It is therefore essential to get your expert evidence right.  To help you, Walker Morris’ Head of Commercial Dispute Resolution reviews recent key case law and shares her own expert advice.

Key cases

Expert evidence has hit the legal headlines several times recently. A spate of cases has dealt with the extent to which expert evidence is required to resolve disputes, the role of the expert in litigation and practical and procedural traps and tactics.  For example:

  • as part of the Royal Bank of Scotland ‘Rights Issue Litigation’ [1], the High Court made some important observations about the court’s duties in relation to expert evidence, as set out in Civil Procedure Rule (CPR) 35.1;
  • in British Airways Plc v Spencer [2] the court comprehensively set out the factors a court will take into account when deciding whether or not to allow expert evidence;
  • in Wattret v Thomas Sands Consulting Ltd [3] the court considered the key principles governing the use, relevance and control of expert evidence, in the context of a professional negligence claim; and
  • in Allen Tod Architecture v Capita Property & Infrastructure[4] the court ordered a party to disclose its original experts’ notes, preliminary report and other documents as a condition of that party being able to change experts.

The facts of these cases are not important for the purposes of this article. What is essential, however, is for anyone involved in a matter which could turn upon expert evidence to note the following legal and practical points arising from the various judgments.

Legal and practical advice

  • It is for the court, not the parties, to determine whether expert evidence is required. The burden of proof lies on the party seeking to adduce the evidence.
  • CPR 35.1 provides that “Expert evidence shall be restricted to that which is reasonably required to resolve the proceedings”. The rule is headed “Duty to restrict expert evidence” and it is expressed in mandatory terms. The message is therefore clear that expert evidence will not be allowed lightly; but how will the court decide whether expert evidence is “reasonably required”?
  • Firstly, what is expert evidence? In the RBS Litigation Mr Justice Hildyard made clear that there must be a recognised body of expertise, governed by recognised standards and rules of conduct, which is relevant to the question which the court must decide. Without that, evidence is not expert evidence, rather it is merely the subjective opinion of a witness. The latter would not be admissible.
  • In addition, an expert must not find facts, attempt to advocate or express what he or she would have done in a particular situation. Rather, he or she must express an expert opinion on the basis of assumed facts.
  • Secondly the court must ask whether expert evidence is necessary – that is, whether a decision can be made without it.
  • If the expert evidence is not strictly necessary, the court will consider whether it will be of assistance. If the evidence will be of assistance to the court, it will be allowed if it is “reasonably required”. At this point the court will consider the facts of the case and a range of influencing factors including:
    • The value of the claim;
    • The effect of a judgment either way on the parties;
    • Who is to pay for the expert;
    • Case management issues, in particular whether allowing expert evidence will cause delay; and
    • Proportionality.
  • If the court concludes that expert evidence is allowed, it can impose case management controls.
  • The court will be concerned to ensure that any evidence adduced is limited to that which is relevant to the question[s] before it. As well as making case management orders limiting the issues which expert evidence may address; requiring single joint experts in appropriate cases; and even mandating the number of pages to which expert reports can run, the court can make adverse costs orders, even on an indemnity basis, against parties seeking to rely on expert evidence which goes beyond.
  • Where a case concerns allegations of negligence on the part of a professional, whilst there is no absolute rule that expert evidence will be necessary, the court will be reluctant to make a finding of negligence without evidence from those within the same profession as to the standard of skill and care expected, and the failure (or otherwise) of the defendant.
  • Litigation privilege is borne out of the principle that a litigant or potential litigant should be able to investigate [potential] disputes and take advice without fear that the results of their enquiries will be disclosable. It covers confidential communications between a lawyer and client, or between either of those and a third party, such as an expert. As such, where litigation is anticipated or ongoing and an expert’s opinion is sought for that purpose, the instructions, the expert’s report and any ancillary documentation will generally be privileged from disclosure.
  • Once an expert has been engaged in accordance with the CPR, even if court proceedings have not yet been issued and the parties are still following a pre-action protocol, the expert owes a duty to the court; and that is irrespective of his or her instruction by a particular party.
  • As the Allen Tod case demonstrates, the expert’s duty to the court means that, if and when a party wishes to rely on a replacement expert, the court will usually only give permission on condition that the party waives privilege in respect of the original expert’s report. Depending on the circumstances of the case, any such disclosure order may also cover the instructions to the expert and any other documents relating to the expert’s opinion.

Experts and privilege – an aside

As an aside, on the important issue of experts and privilege, in a Commercial Court case in 2013 [5] there was insufficient evidence to prove that the documents in question had been produced for the dominant purpose of litigation (a requisite factor for establishing ‘litigation privilege’).  As such, the defendant was forced to disclose documents which revealed its early investigations and thought-processes.

Such a situation can be devastating to a party’s case and yet is a common trap for the unwary. Where a party seeks expert opinion or advice prematurely or without the assistance of a lawyer, there is a real risk that privilege never actually arises.  In those circumstances all information, instructions, expert reports and other related correspondence and documents can be disclosable to the court and to the opposing party.

To avoid getting into such a situation clients should, at the first hint of any dispute, consider what work and investigations may be needed to understand and establish their position. If any expert input is likely to be required, it may be prudent to appoint external lawyers to instruct and deal with the expert adviser[s].

WM Comment

In the current climate of increasingly cost-conscious litigation, parties will be well advised to consider carefully, in every case, whether involving experts in their dispute will genuinely make it quicker and easier for the court to reach a decision on the questions that go to the heart of the case. Any party who attempts to adduce unnecessarily voluminous or irrelevant expert evidence is likely to receive short shrift from the court, and possibly an adverse costs order.

Where expert opinion is required, great care should be given to the identification and appointment of an appropriate expert. That is essential, both to ensure that litigation privilege attaches to communications with experts where possible, and so as to hopefully avoid the need to change experts, and therefore to waive privilege, later down the line.

Where a credible expert is properly instructed and offers an opinion which cuts to the chase, the use of expert evidence can be a valuable dispute resolution tool, which can even facilitate swift settlement.

If you would like any further advice or assistance on the use of expert evidence, or on any dispute resolution issue, please do not hesitate to contact Gwendoline Davies or any member of Walker Morris’ Commercial Dispute Resolution team.


[1] in which a number of institutional investors are suing the bank for losses sustained after they invested in a rights issue in reliance upon an RBS prospectus which allegedly portrayed the bank’s financial health and stability in a more favourable light than was really the case; [2015] EWHC 3433
[2] [2015] EWHC 2477 (Ch)
[3] [2015] EWHC 3455 (TCC)
[4] [2016] EWHC 2171 (TCC)
[5] Starbev GP Ltd v Interbrew Central European Holding BV [2013] EWHC 4038 (Comm)