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[2025] ACTCA 50
respondent. The appeal was dismissed. The appellant was ordered to pay the respondent’s costs of the appeal: [32].
The Court of Appeal dismissed Dr Quach’s appeal against the dismissal of his contempt application. His only formal appeal ground relied on a case about constitutional limits on combining arbitral and judicial powers, which the Court said had no relevance to his appeal. The Court also confirmed that Mossop J’s decision refusing him leave to appear for Bennelong was interlocutory because it did not finally decide Bennelong’s rights in its tax dispute with the Commissioner. The appeal was dismissed, with Dr Quach ordered to pay the Commissioner’s appeal costs.
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2,100 words · generated 06/10/2026
The judgment concerns Dr Michael Van Thanh Quach’s appeal from the dismissal of an application alleging contempt of court by the Commissioner of Taxation. The alleged conduct arose in separate proceedings between Bennelong Medical Pty Ltd and the Commissioner concerning the Commissioner’s treatment of a research and development tax incentive expense. The appeal judgment gives that background briefly and refers readers to [6] of Bennelong Medical Pty Ltd v Commissioner of Taxation [2025] ACTCA 49 for a fuller account: [3].
2 cited instruments linked from this judgment.
The underlying event at the centre of Dr Quach’s application was Mossop J’s decision of 11 April 2023 refusing Dr Quach leave to appear on Bennelong’s behalf. During the Bennelong proceedings, the Commissioner’s counsel and solicitor reportedly described that decision as interlocutory. Dr Quach asserted that the Commissioner’s representatives knew that res judicata could not apply to interlocutory proceedings and had made statements intended to mislead the court: [4], [6], [11].
Dr Quach’s originating application, dated 8 April 2024, sought a finding of contempt, costs, compensatory damages and interest. Its single stated ground was that “[r]es Judicata cannot be applied to interlocutory proceedings”, citing Quach v MLC Life Limited (No 4) [2020] FCA 532 and the authority discussed there: [1]-[2]. The primary judge dismissed the application. She found that Mossop J’s decision was interlocutory, that the statements describing it as such were not false, and that the contempt issue therefore did not arise: [5]-[8].
On appeal, Dr Quach’s sole formal ground was different in terms: “It is not the function of the Court to convert non-judicial to judicial function”, citing Attorney-General (Cth) v The Queen: [13]. The Court of Appeal concluded that this authority had no relevant connection to the appeal. It dismissed the appeal and ordered Dr Quach to pay the Commissioner’s appeal costs: [26], [32].
The Court’s first concern was the mismatch between the stated ground of appeal and the appellant’s submissions. It observed that the written submissions ranged across legal principles that had “no obvious relationship” to the single appeal ground and provided little assistance in identifying the argument: [21]. The oral submissions did not materially clarify the matter: [22].
The Court then examined the authority named in the ground, Attorney-General (Cth) v The Queen [1957] UKPCHCA 1; 95 CLR 529. That case concerned the Commonwealth Court of Conciliation and Arbitration and whether legislation could confer arbitral and judicial functions on the same body. The judgment recounts that the Privy Council affirmed the High Court majority’s conclusion concerning the relevant legislation: [23]-[25]. The Court of Appeal could not discern how that constitutional question helped determine whether the Commissioner’s conduct amounted to contempt in this case. It held that the authority was irrelevant and that the sole ground was not made out: [26].
The Court also addressed the character of Mossop J’s order. It relied on the test expressed by Windeyer J in Hall v Nominal Defendant [1966] HCA 36; 117 CLR 423 at 433: the focus is on whether the order finally determines the rights of the parties in the principal proceeding. Merely deciding an application finally is insufficient, because an order will ordinarily finally decide that application even if the principal proceeding remains unresolved: [30]. The Court also referred to Licul v Corney (1976) HCA 6; 180 CLR 213: [30].
Applying that approach, Mossop J’s decision did not finally determine the rights of Bennelong and the Commissioner in their principal tax proceedings. The refusal concerned Dr Quach’s ability to appear for Bennelong, not the ultimate determination of the parties’ dispute. The later continuation of the principal proceedings, and the fact that Dr Quach was subsequently given leave to appear on a number of occasions, reinforced the lack of finality: [31]. The Court therefore described the decision as interlocutory and said Bennelong required leave to appeal from it: [29]-[31].
These points should be kept distinct. The Court’s conclusion that the underlying order was interlocutory was important to understanding the dispute and was stated clearly. But the appeal was dismissed because the appellant’s actual ground, based on Attorney-General (Cth) v The Queen, did not establish error. The judgment did not decide a general question about when res judicata applies to interlocutory decisions.
The judgment does not purport to change the law on final and interlocutory orders. It applies the approach it attributes to Hall v Nominal Defendant and refers to Licul v Corney as another relevant authority: [30]. Its practical explanation is that the classification depends on the effect of the order on the principal proceeding, rather than simply on whether the particular application has been disposed of.
Before this decision, the primary judge had already treated Mossop J’s order as interlocutory. She reasoned that the order did not finally resolve Bennelong’s rights against the Commissioner and that leave to appeal was consequently required: the appeal judgment summarises those findings at [5], and reproduces relevant reasoning from the primary judgment at [7]. The Court of Appeal agreed with the underlying characterisation, stating that the decision did not finally determine the parties’ rights and that its lack of finality was beyond doubt: [30]-[31].
The decision also explains the effect of describing leave as an “antecedent condition”. Dr Quach challenged the source of power for the primary judge’s use of that phrase. The Court said there was no relevant exercise of power in the statement. The point was simply that the requirement for leave did not bring a prospective appeal to an end; it was a condition to be met before the appeal could proceed: [28]-[29].
The judgment does not announce a new rule about contempt, model litigant obligations, the right of a company officer to appear for a company, or res judicata. Those topics featured in the appellant’s submissions or the history of the originating application, but the Court did not determine them as general legal questions. In particular, the cited proposition about res judicata and interlocutory proceedings was part of the originating application’s stated basis: [2]. The Court did not undertake a substantive analysis of that doctrine or decide its scope.
Accordingly, the “after” position shown by this judgment is a reaffirmation and application of the finality test to the particular order, not a reported alteration to the governing test. The text provided does not establish how other courts later treated this decision.
At [26], the Court said: “The assistance that the appellant seeks to derive from that decision … is not apparent, and was not articulated in any of the submissions.” In plain English, the Court could not see how the constitutional case cited in the appeal ground connected to the dispute it had to decide.
The same paragraph concludes: “The decision has no relevance to the determination of this appeal, and the single ground of appeal relied upon is thus not made out.” That is the decisive treatment of the formal appeal ground. It is not a ruling that every argument raised by the appellant was independently resolved; it is a finding that the only identified ground, supported by that authority, did not establish a basis for allowing the appeal.
At [30], the judgment quotes the test from Hall v Nominal Defendant: the court should ask whether the order “finally determine[s] the rights of the parties in a principal cause pending between them”. It adds that it is not enough to ask whether the order finally decides “the actual application or matter out of which it arises”. In practical terms, a ruling can be final for the particular application but still interlocutory in the larger proceeding.
At [31], the Court applies the test: “On any view of the decision of Mossop J, it did not finally determine the rights of the parties in a principal cause pending between them.” The principal cause was the dispute between Bennelong and the Commissioner. The order about Dr Quach’s appearance did not decide that dispute.
Finally, [32] states the disposition: the appeal was dismissed and the appellant was ordered to pay the respondent’s appeal costs. This is the operative result, separate from the Court’s explanatory reasons.
The judgment is relevant where a party needs to classify an order as final or interlocutory and the order resolves one application while the principal proceeding continues. The key inquiry identified at [30] is whether the order finally determines the rights of the parties in that principal proceeding. A decision that disposes of an application, without finally resolving those rights, may remain interlocutory.
The particular facts here involved a refusal to permit a person to appear for a company in its proceeding against the Commissioner. The Court considered that the refusal did not determine the company’s substantive rights in the tax dispute: [31]. The subsequent continuation of the proceeding, together with later grants of leave for Dr Quach to appear, supported that assessment: [31].
The judgment is also relevant to appeals where the stated ground and the supporting authority may not address the decision under challenge. The Court emphasised that Dr Quach’s range of submissions did not clarify how they connected to his single formal ground: [21]-[22]. It then assessed the authority actually relied on and found it irrelevant: [23]-[26]. The case therefore illustrates the importance, within appellate reasoning, of a discernible connection between the ground of appeal and the legal principle said to support it.
It does not, on the supplied text, establish that every refusal of leave to appear is interlocutory, nor does it resolve every procedural consequence of an interlocutory order. The Court’s conclusion concerns the particular decision and the effect it had on the principal Bennelong proceedings.
The supplied judgment does not describe any later court’s treatment of Quach v Commissioner of Taxation [2025] ACTCA 50. The decision date is 2 December 2025, and the judgment contains no subsequent judicial citations to it. It would therefore be unsupported to say that later courts have followed, distinguished, applied or criticised it.
Within this judgment, the Court refers to and applies earlier authority. It discusses Attorney-General (Cth) v The Queen to explain why that case did not assist the appellant: [23]-[26]. It applies the finality test stated in Hall v Nominal Defendant and refers to Licul v Corney: [30]. It also refers to Bennelong Medical Pty Ltd v Commissioner of Taxation [2025] ACTCA 49 for background to the separate proceedings and for matters repeated in the appellant’s submissions: [3], [15], [27].
Those references show how the Court situated its reasoning, but they are not evidence of later treatment of the 2025 ACTCA decision itself. Any account of subsequent citations or the way later courts used the judgment would require sources beyond the text provided here.
The judgment does not decide the general operation of res judicata in interlocutory proceedings. Although that proposition formed the stated basis of the originating application, the Court’s discussion of the appeal focused on the irrelevance of the authority supporting the single appeal ground and the interlocutory character of Mossop J’s decision: [2], [21]-[26], [30]-[31]. The judgment should not be read as supplying a comprehensive test for when res judicata may apply.
The Court also did not decide whether Dr Quach had standing to bring the contempt application. The reasons record that the primary judge had not made a finding on standing, even though the issue was raised and the respondent indicated that it would not take the point: [12]. That issue therefore remained outside the Court of Appeal’s determination.
Nor does the judgment give a general ruling on when an advocate’s statement in court could amount to contempt, the relevant state of mind, or the scope of any model litigant obligation. Those matters appeared in the history and submissions, but the appeal was disposed of on the basis that the only stated ground did not apply: [16]-[20], [26]. The Court did not decide a broad claim about whether the Commissioner’s representatives had breached such obligations.
The precise reach of the interlocutory-order ruling is also limited by its fact-specific application. The Court applied the principal-cause test to a decision about permission to appear and relied on the continuation of the Bennelong proceedings and later grants of leave: [30]-[31]. The text does not support extending the outcome automatically to orders with different effects on the parties’ substantive rights.
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Source: the ACT Courts (www.courts.act.gov.au). Converted to plain text by ZoeLaw. Not the official version.
SUPREME COURT OF THE AUSTRALIAN CAPITAL TERRITORY COURT OF APPEAL
Case Title: Quach v Commissioner of Taxation Citation: [2025] ACTCA 50 Hearing Date: 29 July 2025 Decision Date: 2 December 2025 Before: McCallum CJ, Kelly and Muller AJJ Decision: 1. The appeal is dismissed. 2. The appellant is to pay the respondent’s costs of the appeal.
Catchwords: APPEAL – PRACTICE AND PROCEDURE – Appeal of dismissal of proceedings – assertion that respondent applied res judicata in interlocutory proceeding – contention as to whether decision of Mossop J interlocutory – assertion of contempt – operation of res judicata – no obvious relationship between legal principles relied upon and single ground of appeal – clear lack of finality in subject decision – appeal dismissed Legislation Cited: Commonwealth Conciliation and Arbitration Act 1904 (Cth) Cases Cited: Attorney-General (Cth) v The Queen [1957] UKPCHCA 1; 95 CLR 529 Bennelong Medical Pty Ltd v Commissioner of Taxation [2025] ACTCA 49 Hall v Nominal Defendant [1966] HCA 36; 117 CLR 423 Licul v Corney (1976) HCA 6; 180 CLR 213 Parties: Dr Michael Van Thanh Quach (Appellant) Commissioner of Taxation (Respondent) Representation: Counsel Self-represented (Appellant) S Wright (Respondent) Solicitors Self-represented (Appellant) Australian Government Solicitor (Respondent) File Number: ACTCA 34 of 2024 Decision Under Appeal: Court/Tribunal: Supreme Court of the ACT Before: Ainslie-Wallace AJ Date of Decision: 16 October 2024 Case Title: Quach v Commissioner of Taxation Citation: [2024] ACTSC 312 THE COURT: Introduction
Dr Michael Van Thanh Quach (the appellant) appeals from the decision of Ainslie- Wallace AJ dismissing his originating application dated 8 April 2024. In that application, the appellant sought the following orders: (a) The Commissioner of Taxation is guilty of contempt by misleading the court (b) Costs (c) Compensatory damages (d) Interests
The originating application identified a single ground in support of the orders sought: (a) Res Judicata cannot be applied to interlocutory proceedings, pursuant to Dr Michael Van Thanh Quach v MLC Life Limited (No 4) [2020] FCA 532 at [24]. Griffiths J referencing Zetta Jet Pte Ltd v The Ship “Dragon Pearl” (No 2) [2018] FCAFC 132, 265 FCR 290 at [14] ff per Allsop CJ, Moshinsky and Colvin JJ).
As the primary judge observed, the background to the originating application that is the subject of this appeal lies in the proceedings between Bennelong Medical Pty Ltd (Bennelong) and the Commissioner of Taxation (the Commissioner): see reasons at [6] in Bennelong Medical Pty Ltd v Commissioner of Taxation [2025] ACTCA 49 for a summary of those proceedings (the Bennelong proceedings), that arise out of a dispute raised by Bennelong as a consequence of the Commissioner’s treatment of a research and development tax incentive expense.
In support of this originating application the appellant read an affidavit sworn by him on 20 May 2024 that provided some brief further explanation of the basis for the application. In that affidavit the appellant contended that at a hearing on 6 September 2023 that was part of the Bennelong proceedings the respondent had, in submissions of counsel, sought to apply res judicata principles in the context of an interlocutory proceeding. The appellant contended that the respondent’s counsel was well aware that those principles had no application to an interlocutory determination.
Decision of primary Judge
In setting out her reasons for dismissing the application the primary judge determined: (a) The decision of Mossop J on 11 April 2023, refusing the appellant leave to appear on behalf of Bennelong was necessarily an interlocutory decision, and leave to appeal from that decision was required. (b) The statements made by counsel and solicitor for the respondent in the course of the hearing before Taylor J on 6 September 2023, to the effect that the proceedings were interlocutory were not false, in fact. As a consequence, no contempt issue arose. (c) That res judicata principles did not impact the outcome of the application.
At [38] of her decision the primary judge observed: In written submissions on the application, the Applicant contended that the Commissioner of Taxation, through his counsel, in stating that the decision of Mossop J was interlocutory “intended to stop the appeal by applying res judicata on interlocutory orders”. He further argued that counsel, Mr Moffett was well aware that res judicata did not apply to interlocutory proceedings through his involvement in two cases, Bennelong Medical Pty Ltd v Commissioner of Taxation [2023] ACTSC 74 and Quach v ATM Residential Pty Ltd [2022] ACTSC 210.
Her Honour’s findings were then set out at [52]-[56]: [52] The High Court and subsequent authorities have emphasised that the determination of whether a decision is final or not rests on the legal effect of the decision. It does not, in my view, rest on the process by which the court was seized of the matter, that is whether it was through a process of seeking interlocutory or final orders. [53] It is pellucidly clear that Mossop J’s decision did not finally determine the rights of the parties to the principal action, being Bennelong and the Commissioner of Taxation. In short, Mossop J’s decision was interlocutory. His decision, in effect, prevented the Applicant from appearing for Bennelong. That the principal proceedings were not concluded by his decision is demonstrated by the fact that in June 2024, Mossop J heard the principal proceedings and dismissed them. [54] That being the case, to bring an appeal against Mossop J’s interlocutory decision required a grant of leave before the appeal could competently be instituted in accordance with s 37J of the Supreme Court Act 1933 (ACT) and r 5310 of the Rules. [55] It follows that the cornerstone of the application for contempt falls away. The statement advanced by Mr Tavolaro in the affidavit filed in the proceedings before Taylor J and the statements of Mr Moffet before her Honour, both to the effect that the decision of Mossop J was interlocutory, were, demonstrably, not false. [56] It follows that the application to have the Commissioner of Taxation dealt with for contempt through making a false statement to the Court will be dismissed.
Accepting the very real difficulty in discerning the case that the appellant sought to make before her, the primary judge appears to have interpreted the appellant’s application as one founded on the premise that the decision of Mossop J on 11 April 2023, refusing the appellant leave to appear on behalf of Bennelong, was not an interlocutory decision, and statements to that effect made by or on behalf of the respondent were thus knowingly false and in contempt of court. She dismissed the application on the basis that the decision was clearly interlocutory and therefore the contempt issue did not arise.
Ground of Appeal
The single ground of appeal relied upon is: It is not the function of the Court to convert non-judicial to judicial function (AG v R and Boilermaker society (1957) 95 CLR 529, 535)
The orders sought on the appeal are: (a) Set aside the judgment of Acting Justice Ainslie-Wallace. (b) Finding that the Commissioner of Taxation is guilty of contempt. (c) Costs. (d) Compensatory Damages.
Submissions
Appellant’s submissions
The argument presented by the appellant in his written submissions bore some close resemblance to that relied upon by Bennelong in its appeal. See reasons in Bennelong Medical Pty Ltd v Commissioner of Taxation [2025] ACTCA 49 at [13].
The appellant sought to compare the role and responsibilities of the respondent to that of a prosecutor. He relied also upon model litigant principles to provide the foundation for a submission that the respondent was obliged to allow Bennelong to proceed in the Bennelong proceedings without legal representation. The appellant referred to interests of justice considerations as a basis for permitting the appellant to be joined in the Bennelong proceedings as an interested party. The appellant noted his entitlement to represent his company in business affairs.
The appellant sought also to rely upon the duty of frankness owed to the Court by counsel representing the respondent. That duty, it was submitted, obligated the respondent, by its Counsel to agree to the setting aside of the decision of the primary judge.
Finally, the appellant relied upon the absence of a source of power for the primary judge to characterise the requirement for leave to appeal in the Bennelong proceedings as an “antecedent condition”.
Respondent’s submissions
The respondent highlighted the narrow compass of the primary proceedings, being in essence a request for a declaration that the respondent was in contempt of court by reason of alleged misleading statements made in the course of the Bennelong proceedings, concerning the interlocutory nature of the decision of Mossop J on 11 April 2023. It described the appeal as nonsensical, observing that it failed to properly raise any issue.
The respondent addressed the single authority relied upon in the notice of appeal and submitted that it had no relevance to this Court's determination of the appeal. Decision
Two observations can be made about the smorgasbord of legal principles comprised in the appellant’s written submissions. First, that they bore no obvious relationship to the single ground of appeal relied upon in the notice of appeal. Secondly, that they provided little assistance in gaining an understanding of the argument to be made on appeal.
Regrettably, the oral submissions at the appeal hearing did not significantly advance the matter.
Dealing with the single ground of appeal, the appellant relies upon the decision of Attorney-General (Cth) v The Queen [1957] UKPCHCA 1; 95 CLR 529 in support of the proposition that the court’s role is not to convert non-judicial to judicial function. That was a decision of the Privy Council on appeal from the High Court. It was concerned with the function and powers of the Commonwealth Court of Conciliation and Arbitration. In that case a majority in the Full Court of the High Court had determined that certain provisions of the Commonwealth Conciliation and Arbitration Act 1904 (Cth) that empowered the Commonwealth Court of Conciliation and Arbitration to order compliance with an order or award, broken or not observed by an organisation, being a power to punish for contempt of its powers and authorities, provided that court with a power that was essentially judicial in character, rendering the relevant part of the Act as invalid. The Commonwealth Attorney General proceeded by way of appeal to the Privy Council.
The Privy Council succinctly stated the issue to be addressed on appeal, at page 536: Is it permissible under the Constitution of the Commonwealth of Australia for the Parliament to enact that upon one body of persons, call it tribunal or court, arbitral functions and judicial functions shall be together conferred? The problem can be solved only by an examination of the Constitution itself. The expression "arbitral functions" is here used to describe compendiously the functions exercisable by the Court other than its judicial functions.
That Court unanimously affirmed the decision of the majority in the High Court.
The assistance that the appellant seeks to derive from that decision, dealing as it does with the constitutional limits of conferral of judicial powers onto non-judicial bodies, is not apparent, and was not articulated in any of the submissions made by the appellant. The decision has no relevance to the determination of this appeal, and the single ground of appeal relied upon is thus not made out.
Other matters raised by appellant
The appellant’s written and oral submissions traversed matters that went well beyond the scope of the single ground of appeal identified above. To the extent that those matters are simply a repeat of the matters articulated in the Bennelong proceedings, we rely on the reasons in that matter at [13].
In this appeal, the appellant raised an additional matter of the source of power for that part of the decision of the primary judge articulated at [59] of her reasons. Her Honour there stated: Of course, the argument that the decision was interlocutory and therefore a grant of leave to appeal was necessary before an appeal could competently be brought, did not bring his appeal to a halt. It imposed an antecedent condition on the Applicant’s appeal, a point Taylor J attempted to make with the Applicant on 6 September 2023.
There was no relevant exercise of power, statutory or otherwise, in that statement. The appellant maintained in his submissions before the primary judge that the decision of Mossop J on 11 April 2023 was a final decision, thus creating a right of appeal without the need for leave. The appellant’s submission was wrong, and Bennelong did require leave to appeal from the decision of his Honour. At [59] her Honour simply addressed the reality that the requirement for leave did not bring the Appellant’s prospective right of appeal to an end, but simply created a condition precedent to be satisfied before the appeal would be allowed to proceed.
That the decision of Mossop J was interlocutory is a matter about which there can be no doubt. In Hall v Nominal Defendant [1966] HCA 36; 117 CLR 423 at 433, Windeyer J observed: In most cases the test that seems to be most satisfactory, and the one that accords most nearly with what has been said on the subject in this Court, is it seems to me to look at the consequences of the order itself and to ask does it finally determine the rights of the parties in a principal cause pending between them. It is never enough to ask simply does the order finally determine the actual application or matter out of which it arises; because, subject to the possibility of an appeal, every order does that, unless it be an order that is expressly declared to be subject to variation. (See also Licul v Corney (1976) HCA 6; 180 CLR 213)
On any view of the decision of Mossop J, it did not finally determine the rights of the parties in a principal cause pending between them. The very fact that subsequent to the decision of his Honour the appellant was on a number of occasions given leave to appear for Bennelong is of itself indicative of the lack of finality in the subject decision.
Orders
Quach
Commissioner of Taxation [2025] ACTCA 50
(1957) 95 CLR 529
The appeal was dismissed. The appellant was ordered to pay the respondent’s costs of the appeal: [32].
Although noting it was unnecessary to do so given her finding set out above, the primary judge also endeavoured to address the res judicata point. She acknowledged some difficulty in understanding the appellant’s submission on this topic: see [57] of the decision of the primary judge.
At [58] the primary judge observed: It seems then that the Applicant’s reference to “res judicata” was to demonstrate that Mossop J’s determination was final “at the level of the Supreme Court” and thus he had an unfettered right of appeal from that decision and, in contending that the decision was interlocutory and therefore to deny him the automatic right of appeal, was done to cause the Applicant harm.
A review of the transcript of the proceedings before the primary judge reinforces the difficulty in relation to the issue of res judicata. On the one hand, the appellant submitted that the solicitor acting for the respondent had filed affidavit evidence in the Bennelong proceedings, wrongly asserting that the decision of Mossop J on 11 April 2023 was an interlocutory decision: see transcript of proceedings dated 14 August 2024, page 5, [20]. On the other hand, the appellant contended that the respondent’s reliance upon res judicata principles in circumstances where it knew that the decision appealed from was interlocutory was an assertion made either intentionally or recklessly to mislead the court: see transcript of proceedings dated 14 August 2024, page 10, [18].
It is noteworthy that the primary judge did not make any finding on the preliminary issue of whether the appellant had any standing to bring this proceeding in circumstances where the conduct complained of occurred in the course of separate proceedings that did not involve the appellant as a party. The transcript reveals that the issue of standing was raised by her Honour, and the respondent indicated that the point was not to be taken.