A matter of expert opinion: how lawyers should engage with expert witnesses

Independent experts are not hired guns engaged to advance a party's position; instead, their overriding duty is to the Court. It follows that any opinions they express are expected to be impartial and unaffected by the wishes of their engaging party and their lawyers. It is, however, commonplace in litigation – for a party seeking to discount the weight of the opponent's expert evidence – to accuse an expert of not being truly independent or not having undertaken or performed their task lawfully or properly. To insulate against the risk of such an accusation, legal practitioners should take considerable care when proffering advice, identifying gaps in reasoning, or directing attention to the relevant issues to be addressed by the expert.

The line between what is permissible and impermissible solicitor advice and commentary has vexed commercial litigants and the courts for some time. In New Aim Pty Ltd v Leung [2023] FCAFC 67, a 5-judge bench of the Full Federal Court provided extensive guidance on these exact issues.

In doing so, it provided important clarification of what is appropriate when giving an expert their instructions and the proper involvement of lawyers in the preparation of expert reports.

Why the expert witness' evidence was rejected at trial…

The applicant New Aim Pty Ltd, is an Australian e-commerce business that sourced its products from suppliers in China. It commenced proceedings against three of its former employees alleging breach of confidence, breach of contract, and a breach of section 183 of the Corporations Act's ban on improper use of confidential information. The claim was dismissed at first instance, including because the evidence of the applicant's expert witness was rejected by the primary judge.

In doing so, the primary judge considered that:

• there was a perceived indeterminable level of interference from the applicant's solicitors in drafting the expert report, with the consequence that the opinions expressed in that report could not be safely relied upon as being the expert's truly held views; and
• the letter of instruction conveyed a false representation. This was because it was dated one day before the expert's report was issued, and thus it carried the false representation that the expert was only then to begin undertaking the task of preparing and drafting a report in response to the questions identified in that letter.

The Full Court disagreed with the primary judge's conclusions and allowed the appeal.

And why the Full Federal Court disagreed: five points to remember for expert evidence

The following key takeaways emerge from the Full Court's decision:

1) The "core" requirement is that lawyers are not permitted to influence the expert's opinion or evidence. Accordingly, lawyers must ensure that they do not, in any interaction with an expert, suggest to the expert what their evidence should be.

2) Subject to (1), there is nothing improper in lawyers:

• drafting factual components of an expert's report; or
• taking instructions and observations from an expert and drafting that evidence in an appropriate and admissible form.

Where lawyers are involved in drafting, it is desirable, although not necessarily essential, to disclose the extent of the lawyer's involvement.

3) The extent of the lawyer's involvement may depend on the area where expert evidence is sought. For example, it would be expected that a medical expert or valuation expert would generally draft their own report, whereas in other contexts, it may be more appropriate for the lawyers to take a greater role in drafting.

4) There is nothing improper or unusual in a letter of instruction being provided contemporaneously or near contemporaneously with the finalisation of an expert report; it is often necessary to engage with an expert to determine the appropriate question(s) to ask to ensure that they do not miss the real issues. This is generally permissible, particularly in areas of specialised knowledge, so long as there is transparency as to the materials provided to the expert and the questions asked of them.

5) There is no legal obligation to disclose all correspondence between lawyers and an expert on the preparation of the report, except where ethical circumstances require otherwise. It is, however, necessary to disclose all instructions given to the expert and ensure that there is transparency in the process undertaken by the expert.