If there is one idea an instructing lawyer or a party facing arbitration for the first time needs to absorb about expert evidence, it is this: the expert works for the tribunal, not for you. Every reputable standard governing expert witness conduct — RICS's Practice Statement, the CIArb Protocol, the IBA Rules on the Taking of Evidence — builds outward from that single principle. This piece looks at what the overriding duty actually requires in practice, and how it plays out specifically in DIAC arbitration and before the DIFC Courts.
What the duty requires, in concrete terms
The overriding duty is often summarised as "independence," but that word understates what is actually being asked of the expert. In substance, the duty requires an expert to:
- State the facts fully, including facts that damage the instructing party's position
- Give an opinion that reflects genuine professional judgment, not the strongest available case for the client
- Disclose the assumptions and instructions underlying the opinion, so the tribunal can weigh them
- Maintain that position throughout the proceedings — including in expert-to-expert meetings and under cross-examination — even where it becomes inconvenient for the party paying the fee
Crucially, this duty does not evaporate because the fee is being paid by one side. RICS guidance is explicit that the duty to the tribunal overrides any contractual duty to the client, and that this holds true whether the expert is independently retained, engaged by an employer on whose behalf they give evidence, or acting as a tribunal-appointed expert. The source of instruction changes nothing about where the loyalty sits once the expert has accepted the appointment.
Why tribunals scrutinise this so closely
Arbitrators and judges who deal regularly with construction disputes see a great deal of expert evidence, and they develop a sharp eye for the difference between an independent opinion and an advocate's brief wearing an expert's clothing. Signs that erode an expert's credibility include:
- Opinions that consistently favour the instructing party on every disputed point, with no acknowledgment of contrary evidence
- Selective use of programme or cost data that omits inconvenient entries
- Reluctance to make concessions during expert meetings that are plainly warranted by the evidence
- A report that reads like a closing submission rather than a technical analysis
None of this needs to be deliberate misconduct to be damaging. An expert who has simply lost sight of where their duty lies — perhaps through long-standing familiarity with the instructing party, or through unconscious alignment with the case theory — can produce evidence that a tribunal ultimately discounts or disregards. The independence requirement exists precisely because this drift is a natural risk, not a hypothetical one.
How this plays out in DIAC arbitration
DIAC's 2022 Rules modernised the institution's procedural framework, and DIAC-administered tribunals increasingly draw on international expert evidence practice, including IBA Rules-consistent expectations around independence and disclosure, even where the IBA Rules are not formally adopted. An expert appearing in a DIAC arbitration should expect:
- Tribunals that are alert to party-appointed expert bias and may test it directly in questioning
- Growing familiarity among DIAC arbitrators with structured expert conferencing and joint statements as tools for narrowing disputed issues
- An expectation that reports will engage with, not simply dismiss, the opposing expert's methodology
How this plays out before the DIFC Courts
The DIFC Courts, including the Technology and Construction Division, operate under a procedural framework more closely aligned with common-law civil procedure than domestic UAE court practice. Expert evidence before the DIFC Courts is subject to rigorous case management, and the Technology and Construction Division in particular handles the kind of complex delay, disruption, and quantum disputes where independence is most likely to be tested. Practitioners appearing before the DIFC Courts should expect:
- Directions that closely regulate the scope and form of expert evidence
- An expectation, consistent with common-law tradition, that experts will narrow issues through structured meetings before trial
- Judicial willingness to give limited or no weight to expert evidence that reads as one-sided advocacy
A practical discipline, not just a principle
For lawyers instructing experts, the overriding duty has a direct practical consequence: an expert who understands and internalises this duty from the outset is a stronger witness, not a weaker one. Instructing counsel should be looking for experts who ask difficult questions of the client's own case, flag weaknesses candidly, and are prepared to say when the evidence does not support the desired conclusion. That candour, delivered early in the engagement, is what produces a report that survives contact with cross-examination — and a client who is not blindsided by their own expert's concessions at the hearing.
Part 3 in this series looks at what an expert must confirm before accepting instructions in the first place — the point at which many of the problems addressed here can be avoided entirely.