In Part 8 of this series, I considered the Expert Witness’s duty to investigate rather than simply accept the factual narrative contained within their instructions. That leads naturally to a related, and in my view more difficult, question. What should an expert do when, during the course of that investigation, they identify something material which falls outside, or perhaps sits at the edge of, the questions they were originally asked to consider?
The phrase “I wasn’t asked to consider that” can sometimes be entirely legitimate. An Expert Witness is not appointed to investigate every aspect of a dispute and should not regard an instruction as an invitation to roam freely across matters outside their expertise or the scope of their appointment. There must be boundaries. The difficulty arises when adherence to those boundaries becomes a reason for ignoring something which materially affects the reliability of the opinion the expert has been asked to give.
This is particularly relevant in construction disputes because the issues seldom exist in isolation. A quantum opinion may depend upon assumptions concerning causation, contractual entitlement or the timing of events. A valuation may depend upon whether work was instructed, undertaken or subsequently omitted. An assessment of loss may depend upon records which reveal something quite different from the factual basis originally presented to the expert. The expert may not have been instructed to determine those underlying matters, and indeed may have no jurisdiction or expertise to do so, but that does not mean they can simply disregard their potential effect upon the opinion they have been asked to provide.
For a quantum expert, this distinction can be especially important. I may, for example, be instructed to value the financial consequences of a particular event on an assumed factual or contractual basis. It is not my function as a Quantity Surveyor to determine a disputed question of law merely because the answer affects my calculation. Equally, however, it would be difficult to justify presenting a single figure as an unqualified expert conclusion if the valuation depends upon a factual or legal assumption which is genuinely disputed. The better approach may be to identify the assumption transparently and, where appropriate, explain the consequences if the Court, Tribunal or adjudicator ultimately determines the underlying issue differently.
That, for me, is where scope and independence intersect. Staying within one’s instructions is important, but an Expert Witness should not allow the wording of those instructions to prevent them from identifying a matter which materially qualifies their opinion. There is a significant difference between expressing an opinion on something outside your expertise and recognising that something outside your remit affects the opinion that is within it.
This distinction can become uncomfortable in practice. An expert may identify a document that neither the instructing solicitor nor the client appears to have appreciated. They may recognise that an assumption upon which a substantial element of the claim depends is questionable. They may discover that the methodology they have been asked to apply produces a result which cannot be reconciled with the contemporaneous records. At that point, “I wasn’t asked to consider that” may be factually correct, but it does not necessarily resolve the expert’s professional responsibility.
In my view, the appropriate response is usually not for the expert simply to expand their remit unilaterally. It is to raise the issue. Explain why it matters. Identify how it may affect the opinion and, where necessary, seek clarification or further instructions. If the matter lies outside the expert’s expertise, say so. If another discipline needs to address it, identify that limitation. What matters is that a material issue is not silently ignored simply because it did not appear within the original letter of instruction.
There is also a danger in allowing the scope of an instruction to become too convenient. An expert report can sometimes appear comprehensive when supporting the instructing party’s position, yet remarkably narrow when confronted with evidence pointing in another direction. That is where a legitimate reliance upon scope risks becoming indistinguishable from selective analysis. The boundaries of an expert’s instruction should operate consistently; they should not expand when an issue assists the client and contract when it does not.
This is something I consider particularly important when reviewing expert evidence in professional negligence and quantum claims. A report may answer the precise question posed to the expert and yet leave the reader with the sense that the real issue has not been addressed. Technically, the expert may be able to say that a particular matter fell outside their instructions. The more important question, however, is whether that matter was sufficiently significant that the expert should at least have identified its existence and explained its potential effect upon the opinion being expressed.
My experience as an adjudicator provides a different perspective on the same issue. When faced with competing expert reports, I am concerned not only with the conclusions reached but also with the assumptions upon which those conclusions depend. Where an expert clearly identifies that their opinion proceeds upon a particular factual or contractual assumption, the decision-maker can take that into account and determine what follows if the assumption is not accepted. The greater difficulty arises where the assumption remains hidden within the analysis. A conclusion may appear definitive when, in reality, it depends upon an issue the expert has never been asked to determine.
That distinction matters because the Expert Witness is not the ultimate decision-maker. There will inevitably be matters of fact or law which the Court, Tribunal or adjudicator must determine. The expert’s role is to provide the technical assistance necessary for those decisions to be made. In many cases, that means recognising alternative factual scenarios rather than attempting to decide between them. An expert may properly say: “If the Tribunal finds A, my opinion is X; if it finds B, the consequence is Y.” That does not weaken the expert evidence. It may considerably increase its usefulness.
Indeed, some of the most valuable expert evidence does precisely that. Rather than presenting an apparently certain answer built upon assumptions that may subsequently fail, it allows the decision-maker to understand the technical consequences of the findings available to them. In quantum disputes this can be particularly effective. An expert can provide alternative valuations or explain how a conclusion changes depending upon particular findings of fact, without straying into the Tribunal’s role by determining those facts themselves.
There is a broader issue here about the relationship between the expert and those instructing them. A carefully drafted letter of instruction is essential, but it cannot anticipate every issue that may emerge during a substantial expert investigation. Expert work is iterative. Documents lead to questions; questions lead to further documents; analysis exposes assumptions; and sometimes that process identifies an issue which nobody appreciated when the original instruction was prepared. That should not be regarded as an inconvenience. It is often evidence that the expert is doing precisely what they were appointed to do.
The danger is when an expert begins to regard the letter of instruction as both the beginning and the end of their professional responsibility. Scope defines the assignment, but it should not become a shield behind which material issues can disappear. If something genuinely affects the reliability of the opinion being expressed, the expert should identify it, explain its significance and deal transparently with any limitation upon their ability to address it.
Ultimately, “I wasn’t asked to consider that” may explain why an expert has not expressed an opinion upon a particular issue. It is less satisfactory if it is being used to explain why the expert failed to identify that the issue materially affected an opinion they were asked to provide.
For me, the distinction comes down to a relatively simple principle. An expert does not have to answer every question in the dispute, but they should recognise the questions upon which their own answer depends.
That is not extending the expert’s remit. It is understanding it properly.
I accept appointments as an Expert Witness and Single Joint Expert in relation to quantum, valuation and construction claims, together with professional negligence claims involving Quantity Surveyors, Contract Administrators and Employer’s Agents.