Most construction and infrastructure disputes proceed with each party instructing its own expert. But tribunals — and parties themselves, by agreement — sometimes opt for a different model: a single expert, jointly instructed or appointed by the tribunal, whose evidence stands in place of competing party-appointed reports. This piece looks at when this approach is used, what it requires of the expert, and why it suits certain disputes better than others.
Why a single joint expert is sometimes the better model
The rationale is straightforward: dealing with a case in a way that puts the parties on an equal footing while minimising cost, without sacrificing the thoroughness the dispute requires. On a discrete technical question — a specific point of structural causation, for example, or a narrow valuation issue where the underlying facts are largely undisputed — the expense and time of two fully developed, competing expert reports can be disproportionate to what is actually in dispute. A single joint expert, instructed by agreement or appointed by the tribunal, can resolve the technical question more efficiently, provided the parties and the tribunal are confident the process will be fair.
This model tends to suit:
- Smaller-value disputes where proportionality is a genuine concern
- Discrete, well-defined technical questions rather than sprawling, multi-issue claims
- Cases where the parties themselves recognise that a jointly trusted expert is likely to produce a more efficient resolution than a battle of competing reports
It tends to suit less well complex, multi-faceted delay and quantum disputes on major infrastructure projects, where the volume of contested facts and the range of plausible technical approaches make a single expert's view a less reliable proxy for what a tribunal, testing both sides' evidence, would ultimately conclude.
What the role requires of the expert
An expert accepting appointment as a single joint or tribunal-appointed expert takes on a role that is, in important respects, more constrained than that of a party-appointed expert. The evidence given must be restricted to what is reasonably required to help the tribunal resolve the proceedings, and this duty overrides any obligation to either party individually. Before accepting the appointment, the expert should be clear on:
- The precise subject matter of the instructions and the extent of the expert evidence actually required
- The specific issues the appointment is intended to address
- How the evidence will be presented, and to whom it will be released
- That the resulting opinions must remain within the expert's genuine area of expertise, and not extend into adjacent questions simply because the appointment invites broader comment
Handling instructions from two parties
One of the more difficult practical aspects of this role is managing instructions that arrive, sometimes inconsistently, from more than one party. Where the expert cannot secure clear or appropriate instructions — because the parties disagree about scope, or because information provided by one side conflicts with information provided by the other — the expert should first attempt to resolve this directly with the parties, and only escalate a request to the tribunal as a last resort, having given the parties reasonable notice before doing so. Directing questions to the tribunal too readily, rather than working to resolve ambiguity constructively, tends to be viewed as a failure of the expert's own case management rather than a legitimate use of the tribunal's time.
Conflicts and disclosure carry particular weight in this role
Because a single joint expert's opinion often carries decisive weight — there being no competing expert view for the tribunal to weigh it against — conflicts of interest and any involvement arising after appointment must be disclosed with particular care. Anything that could give rise to a conflict, or even the public perception of potential bias, should be brought to the attention of the parties and, as appropriate, the tribunal, so that it does not later undermine confidence in the tribunal's eventual findings.
Attending meetings and conferences
A single joint expert should not attend any meeting or conference that is not a joint one — meeting privately with only one party, without the agreement of all parties or a direction from the tribunal permitting it, is inconsistent with the entire rationale for using this model in the first place, and risks compromising the appointment's core value: that all parties can trust the process equally.
A note for private clients weighing this option
For a private client facing a construction dispute of modest value — a residential development defect, for example, or a contained dispute with a single contractor — proposing a single joint expert to the other party, or agreeing to one where it is proposed, can be a genuinely sensible way to control costs, provided the expert selected is one both sides can trust to approach the question with real independence. It is worth discussing this option directly with legal counsel early in the dispute, rather than defaulting automatically to separately instructed experts on both sides.
Part 13 turns to the point at which all of this preparation is tested directly: cross-examination, and how experts prepare to give oral evidence that holds up under scrutiny.