Expert witnesses: key considerations

02 February 2022

In cases which involve highly technical or specific knowledge, or are complicated on a factual basis, it is often necessary to instruct an expert witness to attest to their knowledge in the relevant field and apply this to the facts at hand.

This is far from being a new addition to the litigation process but is one which the courts in England and Wales consider is going to be ever more prevalent. The role an expert witness provides can be truly invaluable to the outcome of a claim, but as with anything the key is getting the best from the opportunity to present that evidence.

So what do you need to bear in mind when instructing an expert?

1. Do you have permission?

First and foremost, you need the court’s explicit permission to enter expert evidence in a matter. Although it is always a consideration early on in the litigation process, you cannot simply assume you can rely on expert evidence to assist your case.

Permission must be sought from the court (either at the stage of directions questionnaires or by making a specific application as required), to allow you to enter an expert’s evidence. Even then, “expert evidence shall be restricted to that which is reasonably required to resolve the proceedings”. There is a general duty to restrict expert evidence and it should be contained to specific points in the proceedings.

2. There are strict rules governing the form of the expert’s evidence

As with witnesses of fact, expert witnesses must follow specific rules in providing their evidence.

An expert’s evidence must take the form of a report and include, for example, details of the expert’s qualifications, a statement setting out the facts and instructions which are material to the expert’s opinion or which their opinions are based upon, and make clear which facts in the report are within their own knowledge.

3. An expert’s report may be used by any party as evidence at trial

Where expert evidence is granted, and the report disclosed, any party may use that expert’s report as evidence as trial. This means that, even, if only one party instructs an expert, both parties can seek to rely on their evidence at trial. This applies even where, perhaps, your expert’s evidence is not fully to your liking.

If a party obtains an expert report and fails to disclose it in evidence, then that party is barred from using the expert’s report at trial. Further, the expert cannot be called to give evidence orally unless permission is granted.

In some cases, the court may order that a single, joint expert be instructed by the parties. In the case of a single, joint expert, both parties may 'instruct' (i.e. write the instructions to the expert separately rather than an agreed letter of instruction prepared between the parties) the expert separately, but a copy of these instructions must be sent to the other party in the interests of openness and fairness. The same is true of any questions raised with an expert following provision of their initial report.

4. The expert’s duties are to the court

An expert’s duty in providing their report, and evidence in general, is to the court. The entire purpose of their evidence is to assist the court on the more technical aspects of a case. This has always been the case, and regardless of which party (or both) has instructed the expert.

There is a prevalence of expert witnesses in the Intellectual Property specialist courts, where the very nature of the subject matter in claims often benefits from an expert assisting the court. 

A recent Intellectual Property Enterprise Court case provides a reminder that expert evidence should be objective but also highlights what the court needs to bear in mind in circumstances where an expert is connected to the party instructing them.

In Tehrani v Hamilton Bonaduz AG and Others [2021]1, HHJ Hacon commented that there is no reason why the chosen expert should not be closely connected to the party they are instructed on behalf of, but warned that the higher degree of proximity to the party there was, may inevitably lead to a risk that the expert’s views could be swayed by loyalty.

Therefore, whilst it is possible to use a 'connected' expert, the court could insist on a higher than usual requirement for the expert to demonstrate that in giving their evidence, their clear and primary duty is in assisting the court.

In Tehrani, the claimant and owner of a patent relating to a medical ventilation device, chose to act as her own expert witness. The Judge found that the claimant had not provided the necessary indication of her objectivity in giving expert evidence, ultimately leading to the patent in question being declared invalid.2

5. Last thought: expert evidence and a lesson from COVID-19

Over the last two years the courts have had to adapt to ensure claims to progress despite the restrictions on in person gatherings and meetings in enclosed spaces. Although remote evidence has been used in some court hearings for a number of years it was not particularly commonplace. Out of necessity, the courts have allowed witnesses to give evidence remotely via video link, including experts, in order to keep the judicial system moving.

Although we are seeing a gradual return to the courtroom for hearings, witness evidence and trial, it is obvious that there are benefits to remote attendance for witnesses generally. Some legal professionals will tell you there is nothing that compares to a witness being physically present and giving their evidence in person. But in a world where the effects of a pandemic have forced the hand of our legal system to adapt, should this revert back from the 'new normal'?

Mrs Justice Falk, in a lecture delivered towards the end of 2021, recognised that “in more substantive hearings with witness evidence, some witnesses… may well continue to give evidence remotely… This will particularly be the case with expert witnesses.”

She also commented, in a reflection that has perhaps been teased out in the court’s lack of choice in having to use video links for evidence, that “it is in fact possible to assess credibility remotely when necessary to do so. The idea that this is done to any material extent by reference to a person’s physical demeanour is… generally regarded as outdated.” [Ibid]

Expert witnesses are usually professionals within their field, and many have previous experience of giving evidence in court proceedings, so the assessment on credibility (whilst it can obviously never be said to be discounted) may not be as crucial as for witnesses of fact in the case.

If you wish to discuss any of the issues outlined in this article, then please contact Jessica Mason or another member of the Litigation and Dispute Resolution Team.

1 EWHC 3457 (IPEC)
2 Ibid, paras 6-10.

The content of this article is for general information only. It is not, and should not be taken as, legal advice. If you require any further information in relation to this article please contact the author in the first instance. Law covered as at February 2022.



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