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Begging for permission: expert evidence

Posted on 24 November 2023

It has famously been said that the UK has had enough of experts, but the High Court has recently provided its own helpful summary of when it will grant permission for the use of expert evidence in a case.

In Wambura & Ors v Barrick TZ Ltd & Anor [2023] EWHC 2582 (KB) the claimants sought permission to call expert evidence on security and risk assessment issues in relation to claims for personal injury and death, suffered in the context of civil unrest at a gold mine in Tanzania. In declining permission, the Master outlined the relevant considerations for whether a court will allow expert evidence.

Expert evidence is an exception to the general rule

It is often forgotten in complex commercial cases that the standard position on evidence is that only evidence of fact (such as witness statements from relevant people involved) may be adduced to the court. Expert evidence, which is evidence of opinion rather than fact, is an exception to that general position but the court's permission must be obtained before a party can call an expert. The Master in Wambura confirmed that the court "should not be shy about limiting the occasions" when expert evidence is permitted. Indeed, CPR Part 35, which governs the use of expert witnesses, makes it explicit that the court has a "duty to restrict expert evidence".

The legal tests

Permission for expert evidence will only be given if: (i) the evidence is admissible and (ii) it is "reasonably required to resolve the proceedings". The Master in Wambura acknowledged that the tests for each of these conditions overlap significantly.


In Kennedy v Cordia (Services) LLP [2016] UKSC 6 (an appeal from the Scottish Court of Session), the Supreme Court identified four considerations governing the admissibility of expert evidence:

  1. Whether the proposed expert evidence will assist the court in its task;
  2. Whether the witness has the necessary knowledge and experience;
  3. Whether the witness is impartial in their presentation and assessment of the evidence; and
  4. Whether there is a reliable body of knowledge or experience to underpin the expert’s evidence.

The party seeking permission must satisfy the Court as to all four considerations.

As to the first consideration, in Wambura, the Master confirmed that the party proposing to adduce expert evidence must be clear as to precisely what the expert's task will be. Repeatedly changing the expert's terms of reference (or draft instructions) or requesting evidence on topics that are too wide or unfiltered will not be acceptable.

Even where the proposed evidence is focused, it must genuinely assist the court. The Master agreed with a range of decisions that have noted that the court is perfectly capable of making findings of fact where the issues are not especially technical. Even where there are relevant independent standards governing the area of proposed expertise, if those standards are generalised and written in plain non-technical language, the court will not necessarily be assisted by expert evidence in interpreting them (as was the case here with the UN Voluntary Principles on Security and Human Rights).

Both the second and third considerations will be decided on the facts. However, as part of her analysis of the witness's expertise (the second consideration), the Master indicated that the fact that the proposed witness had never acted as an expert witness before should not itself be a limiting factor, as every proficient witness has to start working on a first instruction.

The fourth consideration may overlap with the first, in that whether there is a reliable body of knowledge is also relevant to whether expert evidence would assist in interpreting that body of knowledge. "Reliable body of knowledge" is not confined to rules and practices of professional institutes but relates to "accepted standards of conduct sanctioned by common usage". The Master endorsed a previous rulingwhich stated that unless there is such a recognised body of knowledge, the intended witness would be giving their subjective opinion rather than expert evidence, rendering the evidence inadmissible.

Reasonably required to resolve the proceedings

If the court finds that expert evidence is admissible, it will still be necessary to demonstrate that it is reasonably required to resolve the proceedings. British Airways PLC v Spencer [2015] EWHC 2477 (Ch) established a three-stage test to evaluate that question:

  1. Is the expert evidence necessary to decide an issue, rather than merely helpful? If yes, it should be allowed;
  2. If it is not necessary, will it assist the judge in determining an issue? If it would assist but is not necessary then the court should consider stage three, namely;
  3. If expert evidence on that issue was reasonably required to determine the proceedings.

In answering the third question, consideration needs to be given to the value of the claim and proportionality, the effect of a judgment either way on the parties, the cost of the evidence and who will pay for it, and whether any delay will be caused, or a trial date lost.

Determining whether expert evidence is necessary, or merely helpful, may be a difficult question and will inevitably be dependent on the circumstances of the case. In Wambura, the Master found that the evidence was not necessary, because the issues were within the competence of a trial judge to determine. She also held that expert evidence would not be helpful as it would be merely opinion evidence, and accordingly was not reasonably required to resolve the proceedings.


Parties to a claim should consider carefully whether there is a real need for expert evidence to resolve the issues in their case. In light of the decision in Wambura, it is helpful to remember that the courts will not wave through applications to adduce expert evidence and that strict criteria apply.

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