Posted on April 28, 2026 by Liam Mulligan and Tim Lawson 3

Expert Evidence in Judicial Review Proceedings

Ordinarily in judicial review proceedings, evidence which was not before the original decision-maker cannot be relied on to challenge the validity of the relevant decision. This is because judicial review is concerned only with the lawfulness of a decision and any assessment of merits is generally impermissible and the Court is not determining whether or not it would have made the same decision had it been the decision-maker.

However, there is no statutory or general rule precluding the admission of expert evidence in judicial review proceedings and there are exceptions to the general prohibition referred to above. One key exception is when expert evidence is relied upon to demonstrate that an administrative action or decision was legally unreasonable or irrational.  In two recent cases of the NSW Land and Environment Court, a party sought leave to submit fresh expert evidence by relying on this exemption and alleging the Council had acted unreasonably in reaching the decision under review.

Background

In Mulpha Hotel (Sydney) Pty Ltd v Council of the City of Sydney (Mulpha), the Applicant for judicial review alleged that it was legally unreasonable for the Council to form a view that a right of carriageway (ROC) could remain operational during the construction of the approved development.

The Applicant sought to rely on the expert evidence of a structural engineer, which was intended to assist the Court in understanding the structural integrity of the existing structures within the ROC, which the Applicant alleged ought to have been before the Council.

In Fred Caterson Champions v The Hills Shire Council (Fred Caterson), the Applicant alleged that the Council had failed to examine and take into account matters affecting or likely to affect the environment in accordance with its statutory obligation under s5.5 of the Environmental Planning and Assessment Act 1979 (EPA Act).

The Applicant sought to adduce an ecology report dealing with an owl population at the site, to demonstrate that the Council had failed to make reasonable inquiries into relevant environmental matters – in particular the impact of the approved development on the native owl population.

The issue for determination in both cases turned on whether the expert evidence was necessary to determine if the impugned decisions were legally unreasonable.

Decisions

Mulpha

The Court held that the expert evidence was not reasonably required to determine the real issues in dispute, and the application for grant of leave was refused.

In reaching this conclusion, the Court referred to key principles governing the admissibility of new expert evidence in judicial review proceedings:

• generally, only the material that was before the original decision-maker is relevant. This is because judicial review is concerned with the lawfulness of the decision under review and any “trespass” or “slide” into the merits of the decision is to be avoided (Botany Bay City Council v Minister for Planning and Infrastructure[2014] NSWLEC 14 at [7]);
• expert evidence may be admitted in judicial review proceedings but the mere fact that expert evidence is potentially relevant is not sufficient for leave to be granted (Muswellbrook Shire Council v Hunter Valley Energy Coal Pty Ltd[2017] NSWLEC 184 at [42]);
• rather, the evidence must be “reasonably required” to resolve the issue and the admission of the evidence must facilitate the just, quick and cheap resolution of the real issues in the proceedings (Shellharbour City Council v Minister for Planning[2011] NSWCA 195 at [35]);
• there are exceptional cases which depend upon the grounds of review, the nature of the evidence proposed to be called, and the particular facts and circumstances of the proceedings (Nature Conservation Council of NSW Inc v Minister for Water, Property and Housing [2022] NSWLEC 69 at [26]).

The Council had prepared demolition plans based upon the report of a structural engineer and therefore, the Court held, it could not be said that the approval was granted by the Council in the absence of any structural engineering material before it. The Applicant also did not provide the Council with any structural engineering materials or materials that took particular issue with how the ROC would be protected during demolition works.

Consequently, the new structural engineering evidence was not reasonably required to determine the ROC issue, as the alleged legal unreasonableness of the decision could be assessed on the materials that were before the Council.  Absent any exceptional circumstances, this would require the Court to engage in impermissible merits review by determining whether the ROC could remain operational during the development.

Fred Caterson

The Court determined that the Applicant’s owl ecology report was admissible as it weighed on the issue of whether the Council had acted unreasonably by failing to make inquiries into matters affecting or likely to affect the environment pursuant to s5.5 of the EPA Act.

Although substantial parts of the report did provide an assessment of merits, it was also relevant to the inquiries that ought to have been undertaken. There was clear evidence before the Council of a pair of resident breeding Powerful Owls in the reserve adjacent the subject site, and the report expressed that it would have been reasonable to conduct a more detailed assessment of the likely effect of the development on that pair, particularly from light spill on its habitat. Without the report, the Court would have no evidence before it about what inquiries an expert might undertake, which in this case lead to the conclusion that it was legally unreasonable not to make the asserted inquiry.

The question of whether particular expert evidence will be admissible in judicial review proceedings requires a fine-grained analysis of the grounds of review, and the potential probity of the evidence to a fact in issue. It is not simply the case that such evidence not before the original decision maker will never be admitted in judicial review proceedings.

You can read the full text of the judgments here:

• Mulpha Hotel (Sydney) Pty Ltd in its capacity as trustee of the Mulpha Hotel Sydney Trust v Council of the City of Sydney [2026] NSWLEC 23
• Fred Caterson Champions Inc t/as Fred Caterson Champions v The Hills Shire Council [2026] NSWCA 68

If you have any questions regarding this article, please leave a comment below or contact Liam Mulligan on (02) 8235 9715 or Timothy Lawson on (02) 8235 9725.