The proposition is trite but sometimes overlooked.
A modern High Court migration authority for this proposition can be found in SZBEL v Minister for Immigration (2006) 228 CLR 152, [25].
In BMF16 v Minister for Immigration [2016] FCA 1530, Bromberg J said at [222]-[224]:
222. In Ucar, following a comprehensive survey of the authorities, Redlich JA (with whom Warren CJ and Chernov JA relevantly agreed) stated (footnotes omitted):
In my view, the principle laid down in Stead contemplates two circumstances in which relief may be refused. It will be refused if upon analysis of the basis for the decision there is an incontrovertible fact or point of law which provides a discrete basis for the decision which cannot be affected by the procedural unfairness. It will then be concluded that the applicant could not possibly have obtained a different outcome. Second, even where the subject of the procedural unfairness touched upon an issue in dispute that was material to the decision, relief may be refused if the respondent can demonstrate that it would be futile to hold a further trial because the result would inevitably be the same.
223. As to the first circumstance contemplated by Stead and referred to by Redlich JA, there is no incontrovertible fact or point of law which provides a discrete basis for G’s refusal decision which is not affected by the procedural unfairness which I have found. As for the second circumstance contemplated in Stead, it was for the Minister to demonstrate that it would be futile to set aside G’s refusal decision because on a reconsideration, the result would inevitably be the same (as to that onus see also Hayne J in CSR Limited v Della Maddalena [2006] HCA 1; (2006) 80 ALJR 458 at [109]).
224. In any event, and putting aside questions of onus, as McHugh J said in Re Refugee Review Tribunal; Ex Parte Aala [2000] HCA 57; (2000) 204 CLR 82 at [104] (in a passage later referred to by the Full Court in VAAD v Minister for Immigration and Multicultural and Indigenous Affairs [2005] FCAFC 117 at [80]), “once a breach of natural justice is proved, a court should refuse relief only when it is confident that the breach could not have affected the outcome”. Where the issue is whether additional evidence and submissions could have affected the outcome of the decision-maker’s consideration of the matter, it cannot normally be said with certainty that affording such an opportunity was futile: VAAD at [81] citing Kirby J in NAFF at [85]. It will be “no easy task” (Stead at 145) to satisfy a court that a denial of natural justice could have had no bearing on the outcome.
The reference to Aala was most recently re-endorsed in Gill v Minister for Immigration and Border Protection [2017] FCAFC 51.