As outlined in the Expert Witness Code of Conduct in each jurisdiction, an expert’s duty is to the court and the independence of their opinion is crucial. Any input from another person that could potentially compromise that independence or otherwise influence the opinion of the expert is wholly inappropriate and has the potential to make the report inadmissible and risk disciplinary action for the expert and the party who influenced the opinion.
Nevertheless, many experts, particularly those new to the process of expert witness report writing, may have little or no understanding of the legal requirements their report must meet in order to be admissible, and may potentially benefit from their instructing solicitor suggesting edits.
Once an expert witness has completed a first draft of their report, it is a delicate balance regarding the suitable amount of input for a lawyer to have on further drafts. Although it is acceptable for lawyers to provide suggestions to expert witnesses on how to improve their report, to ensure admissibility requirements are met, it is vital to ensure that any changes made are not substantive changes to the expert’s opinion, or else risk having the entirety of the expert report rejected.
The Case Law
Cases where the editing of expert reports have been performed by a lawyer or barrister have been addressed by the courts in a number of decisions.
In Phosphate Co-Operative Co of Australia Pty Ltd v Shears, Brooking J observed:
“The guiding principle must be that care should be taken to avoid any communication which may undermine, or appear to undermine, the independence of the expert.” 
An example of inappropriate interference is found in Universal Music Australia Pty Ltd v Sharman License Holdings Ltd, in which the conduct of a solicitor in suggesting changes to a draft expert report was deemed to have compromised the expert’s independence.
The draft showed exchanges between the expert and a solicitor who had crossed out a sentence in the draft and suggested a substitute sentence with alternative information. The expert replied: “I was not aware of [that information], even after our testing. But if you say it is so, then fine by me”. He then left the solicitor’s words in the draft.
Based on the expert’s responses about this exchange under cross examination, Wilcox J concluded that the expert “was prepared seriously to compromise his independence and intellectual integrity” and that it would be unsafe to rely on his evidence in relation to any “controversial matter”. 
The clearest statement about issues of input into draft reports was by Lindgren J in Harrington-Smith v Western Australia (No 7).  In this matter, his Honour was dealing with a number of different expert reports, some of which had significant deficiencies of form, such that “little or no attempt seems to have been made to address in a systematic way the requirements for the admissibility of evidence of expert opinion”. 
In discussing the contributions by counsel in such situations, his Honour stated that:
“Lawyers should be involved in the writing of reports by experts; not, of course, in relation to the substance of the reports (in particular, in arriving at the opinions to be expressed); but in relation to their form, in order to ensure that the legal tests of admissibility are addressed” (emphasis in original).
Justice Lindgren further indicated that, while it is commendable for lawyers to avoid any suggestion of improper influence on the expert, it should be easy enough for the court to make the distinction between matters of form and those of substance:
“I suggest that the distinction between permissible guidance as to form and as to the requirements of [admissibility under] the Evidence Act, on the one hand, and impermissible influence as to the content of a report on the other hand, is not too difficult to observe. It does not serve the interests of anyone, including those of the expert witness, to deny him or her the benefit of guidance of the kind mentioned. 
These comments were endorsed by the Full Court of the ACT Supreme Court in R v Coroner Maria Doogan. In that matter, the prosecution argued that counsel for the first defendant had improperly interfered with the preparation of an expert witness report and, as a result, had adversely affected the impartiality of the expert. Higgins CJ, Crispin and Bennett JJ stated that:
“[T]he mere fact that some editing of [expert reports] occurred does not demonstrate any impropriety on the part of the lawyers in question or provide any valid ground for concern…[T]hose assisting the first respondent [had a] duty to ensure that the reports conveyed the author’s opinions in a comprehensible manner, that the basis for those opinions was properly disclosed and that irrelevant matters were excluded.” 
These judgement provide a useful reminder that there is a role to be performed by legal advisers in advising on matters of form that may strengthen the expression of an expert’s opinion, so long as there is no attempt to change or influence the actual opinion of the expert. Lawyers would be advised to keep in mind that impelling an expert to reverse or otherwise change their evidence can lead to whole reports being rendered inadmissible, among other serious consequences.
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  VR 665 at 683:30.
  FCA 1242 at -.
  FCA 893.
 Ibid at .
 Ibid at .
 Ibid at .
  ACTSC 74 at .