LEAVE TO APPEAL - RELEVANT PRINCIPLES
13 An applicant for leave to appeal must generally demonstrate: first, that the decision in question is "attended with sufficient doubt to warrant its being reconsidered by the Full Court"; and second, that "substantial injustice would result if leave were refused, supposing the decision to be wrong": Re Décor Corporation Pty Ltd and Rian Tooling Industries Pty Ltd v Dart Industries Inc (1991) 33 FCR 397; [1991] FCA 844 at 398 (Sheppard, Burchett and Heerey JJ); Advanced Holdings Pty Ltd v Commissioner of Taxation (2020) 281 FCR 149; [2020] FCAFC 157 at [35] (Steward J, with Allsop CJ and Bromwich J agreeing); Davidson v Official Receiver [2021] FCAFC 73 at [15] (Allsop CJ, Markovic and Anastassiou JJ). The two criteria are cumulative and both must ordinarily be made out: Rawson Finances Pty Ltd v Deputy Commissioner of Taxation [2010] FCAFC 139 at [4]-[5] (Ryan, Stone and Jagot JJ); Ah-Chee v Stuart [2019] FCAFC 165 at [12] (Reeves, Griffiths and Charlesworth JJ). They are also related and should not be divided into "separate compartments": Ah-Chee at [12]; Cabcharge Australia Ltd v Australian Competition and Consumer Commission [2010] FCAFC 111 at [20] (Kenny, Tracey and Middleton JJ).
14 While the two Décor criteria may not represent a "hard and fast rule" (Samsung Electronics Co. Ltd v Apple Inc. (2011) 217 FCR 238; [2011] FCAFC 156 at [29] (Dowsett, Foster and Yates JJ)), they nevertheless provide "general guidance which the Court should normally accept": Rawson Finances Pty Ltd v Commissioner of Taxation [2016] FCAFC 95 at [39] (Robertson, Moshinsky and Bromwich JJ).
15 In relation to the first of the two Décor criteria, an applicant for leave to appeal does not have to demonstrate that the proposed grounds of appeal are strongly arguable, or that the proposed appeal will or is likely to succeed. An applicant need only demonstrate that there is sufficient doubt about the correctness of the decision to warrant appellate reconsideration. Where, however, the decision of the primary judge is a discretionary decision, the applicant will generally need to demonstrate that the doubts as to the correctness of the decision involve errors or matters of principle of the kind described in House v The King (1936) 55 CLR 499; [1936] HCA 40 at 504-505 (Dixon, Evatt and McTiernan JJ). It will generally not be sufficient to merely demonstrate that the discretion could or even should have been exercised differently because, for example, the relevant considerations could or should have been weighed differently to the way they were weighed by the primary judge: Ah-Chee at [13]; Construction, Forestry, Mining and Energy Union v Australian Competition and Consumer Commission (2016) 242 FCR 153; [2016] FCAFC 97 at [16]-[17] (Dowsett, Tracey and Bromberg JJ).
16 As for the second of the Décor criteria, an applicant seeking leave to appeal an interlocutory decision is likely to suffer substantial injustice, supposing the decision to be wrong, if the decision has the practical effect of finally determining the rights of the parties, or determines "a substantive right": Décor at 400. The existence of those circumstances will generally provide a prima facie case, or at least a strong ground, for the grant of leave to appeal: Ex parte Bucknell (1936) 56 CLR 221 at 225-226 (Latham CJ, Rich, Dixon, Evatt and McTiernan JJ); Construction, Forestry, Maritime, Mining and Energy Union v One Key Workforce Pty Ltd [2020] FCAFC 27 at [44] (McKerracher, Farrell and Markovic JJ); Hastwell v Kott Gunning [2021] FCAFC 70 at [26], citing Johnson Tiles Pty Ltd v Esso Australia Pty Ltd (2000) 104 FCR 564; [2000] FCA 1572 at [43] (French J, with whom Beaumont and Finkelstein JJ agreed); Aardwolf Industries LLC v Tayeh [2020] NSWCA 301 at [1] (Bell P), [54] (Macfarlan JA) and [87] (Leeming JA).
17 Different considerations generally apply, however, where the decision in question is a discretionary decision relating to a matter of practice and procedure and no questions of general principle are at stake. In such cases, appellate intervention requires the "exercise of particular caution": Hogan v Australian Crime Commission (2010) 240 CLR 651; [2010] HCA 21 at [34] (French CJ, Gummow, Hayne, Heydon and Kiefel JJ). In Adam P Brown Male Fashions Pty Ltd v Phillip Morris Incorporated (1981) 148 CLR 170 at 177, Gibbs CJ, Aikin, Wilson and Brennan JJ approved the following "oft-cited" statement of Sir Frederick Jordan in In re the Will of F. B. Gilbert (dec.) (1946) 46 SR (NSW) 318 at 323:
… there is a material difference between an exercise of discretion on a point of practice or procedure and an exercise of discretion which determines substantive rights. In the former class of case, if a tight rein were not kept upon interference with the orders of Judges of first instance, the result would be disastrous to the proper administration of justice. The disposal of cases could be delayed interminably, and costs heaped up indefinitely, if a litigant with a long purse or a litigious disposition could, at will, in effect transfer all exercises of discretion in interlocutory applications from a Judge in Chambers to a Court of Appeal.
18 It is convenient to first address whether it can be said that Mr Roberts-Smith would suffer substantial injustice supposing that the judgment of the primary judge was wrong.