Expert evidence is a common and, in most instances helpful, feature of modern litigation and arbitration. Daniel Turner works with Alison Ross and Mark Harper QC from Kings Chambers to explain the challenges facing expert witnesses.

With disputes becoming more complex, courts and arbitration tribunals remain reliant on expert evidence. However, both judges and arbitrators are not reluctant to refuse the admission of expert evidence where it doesn’t comply with the rules governing the relevant proceedings.

In this series of articles, we worked with Kings Chambers to address a number of the requirements of an expert witness and the challenges they can face in fulfilling this role effectively. In this first article, we explore the expectations made of the expert and the importance of establishing at the outset how the expert will transition from adviser to witness.


Expectations of expert witnesses

First and foremost an expert witness is not an advocate for his or her client, a fundamental concept that instructing lawyers are aware of, but often the client is not.

In our experience, clients can range from small owner-managed businesses through to blue-chip companies. With that comes not only varied levels of experience and previous exposure to litigation, but also varied levels of emotional investment in the process and expectations of all professional advisors engaged within the process.

When appointed in the role of expert in court proceedings or arbitration, an expert must comply with the rules relevant to the jurisdiction and proceedings, for example the Civil Procedure Rules (‘CPR’), Part 35 – Experts and Assessors, when a matter is heard in the courts in England and Wales.

It’s important for instructing solicitors, and appointed experts where necessary, to educate the client on the role of the expert and the expert’s duty to the court or tribunal, which overrides any duty to the instructing party or parties. To put it succinctly, the role of the expert witness is not to articulate or advocate the position of the lay client, rather it is to assist the ultimate decision-maker.


The role of expert witnesses

While the role and responsibilities of the expert are clearly presented in Part 35 of the CPR for matters heard in the courts of England and Wales, there are other jurisdictions where guidance may not be as prescriptive.

To see how the role of an expert has been described in the most quoted English court judgment on the matter, one should review the judgment of Mr Justice Creswell in National Justice Compania Naviera SA versus Prudential Assurance Company Limited (commonly referred to as the ‘Ikarian Reefer’ case, [1993] 2 Lloyd’s Rep. 68).

Among the areas addressed in this judgment, the following two key statements presented by Cresswell J are particularly relevant to what is expected of the expert:

‘An expert witness should state the facts or assumptions upon which his opinion is based. He should not omit to consider material facts that could detract from his concluded opinion’.

In our experience, lay clients sometimes express concern that matters that may be contrary to the position that they have presented or unfavourable to the overall position of the case have been considered by the expert. We often have to emphasise to these clients that an expert’s overriding duty sometimes requires the expert to act in a manner that doesn’t match a client’s expectations or doesn’t support all elements of a client’s pleaded case.

‘In cases where an expert witness, who has prepared a report, could not assert that the report contained the truth, the whole truth and nothing but the truth without some qualification, that qualification should be stated in the report’.

In certain matters, it’s necessary to include a limitation of scope section in expert reports where the lay client, or the opposing client, has not been able to provide the required information or granularity of information to allow a full independent review and/or opinion to be drawn in respect of certain aspects of a claim. Clients are naturally reluctant for the inclusion of any such limitations, and while rare, such wording is necessary if the limitation of scope is relevant to the overall conclusions reached.

When seeking to explain an expert’s approach and duties to a client, it’s beneficial to refer back to the guidance provided by Lady Justice Carr in Secretariat Consulting PTE Ltd & Ors versus A Company ([2021] EWCA Civ 6), which neatly encapsulates an expert’s duty:

‘…an expert who complies fully with his duty of independence and objectivity to the court or arbitral tribunal is an expert who provides his client with the best possible service’.


The question for expert witnesses

The question that needs to be asked and answered at the outset, is what role is the expert to perform? If the role is to be that of providing expert advice and assistance in the investigation and formulation of a claim, then the expert is not subject to the rules referred to above. If the role is to be that of expert witness, then the expert is subject to the rules.

The expert as adviser is an important role. Early engagement with the expert can inform as to, for example, the investigation of and formulation of a claim, estimating the value for the purposes of early alternative dispute resolution (ADR), client document management for the purposes of disclosure and subsequent expert reports and informing a team as to the disclosure to be sought from the other parties.

Often an expert will be brought in at the outset to provide advice in connection with proposed litigation but with a view to that expert becoming the party’s expert witness in the litigation. If this is the expectation, then it needs to be communicated at the outset and plans put in place as to when and how the expert will transition from expert adviser to expert witness.

Unless there is a clear and provable demarcation, the expert will face difficulties in being able to identify (both for its own purposes and those of the tribunal) what has been relied upon for the purposes of the report. In this regard, CPR 35.10 is relevant as it provides that the expert must identify in the report the material instructions that have been received. To address this the common approach is to issue separate retainer letters for the advice and witness retainers (see CPR 35E-GB paragraphs 4 – 8).

While there is no bar to an expert acting as adviser and then as expert witness, this is subject to the fundamental principle underlying CPR Part 35 and the role of an expert witness namely that of independence.


Avoiding compromised advisers

Even though it might have always been envisaged and planned that an expert will transition from adviser to witness, the question still has to be asked (both by expert and instructing party) as to whether or not anything has occurred during the advice retainer that has compromised the independence of the expert.

As with any previous relationship/connection with a client/a dispute, the expert needs to ask and answer the question as to whether or not there is anything arising from the advice retainer that impacts on the ability to act as expert witness.

This further demonstrates the need to plan from the outset how the expert will transition from adviser to witness. Such plans will include taking steps to minimise the risk of the expert’s ability to act as a witness being compromised.

To this end, it would be reasonable to expect the advice retainer letter to specify the specific tasks to be undertaken by the expert and for those to be limited to specific tasks that require or may require expert input.

Further considerations will be the extent to which information relating to the litigation (including the underlying dispute) is shared with the expert and the extent to which the expert has interaction with the client or is a party to legal team meetings, etc; in short, the approach has to be about ensuring that the expert does not become part of the story of the litigation.

If there is proper demarcation between the role of expert adviser and expert witness and a plan put in place and followed to ensure that both roles can be performed without one compromising the other, then the client stands to benefit from the best possible expert service.

To learn more about the role of the expert witness contact Daniel Turner.

To get in touch with Mark Harper QC, please contact his clerk Gary Young at [email protected]


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