Natural JusticeNatural justice is a general court term for a profound breach of civil justice, typically one that need not be accompanised by prejudice to a party to be actionable. It bears a close relation to the administrative concept of 'fairness', as that latter concept is being used to flesh out the rules of admin law. It's hard to find a natural justice issue that doesn't have a counterpart issue under the heading of administrative 'fairness', or at least hasn't been codified already in the Rules of Civil Procedure or otherwise.
. R v Olusoga
In R v Olusoga (Ont CA, 2019) the Court of Appeal reiterated the principle that a miscarriage of justice grounds an appeal even though no prejudice is shown:
 We agree with duty counsel that the appeal must be allowed and a new trial ordered. It is well-established that “a miscarriage of justice need not always be supported by the demonstration of actual prejudice to an appellant; sometimes, public confidence in the administration of justice is just as shaken by the appearance as by the fact of an unfair proceeding”: R. v. McDonald, 2018 ONCA 369 (CanLII), 360 C.C.C. (3d) 494, at para. 51 (quoting from R. v. Kankis, 2012 ONSC 378 (CanLII), 281 C.C.C. (3d) 113, at para. 37); see also R. v. Cameron (1991), 1991 CanLII 7182 (ON CA), 2 O.R. (3d) 633 (C.A.), at pp. 638-39; R. v. Morrissey (1995), 1995 CanLII 3498 (ON CA), 22 O.R. (3d) 514 (C.A.), at pp. 541-42.. Hearn v. McLeod Estate
In Hearn v. McLeod Estate (Ont CA, 2019) the Court of Appeal held that reliance on unadmitted evidence by the trial judge was a breach of natural justice:
 ... The first is a breach of the rules of natural justice. In Pfizer Co. v. Deputy Minister of National Revenue (Customs & Excise), 1975 CanLII 194 (SCC),  1 S.C.R. 456, the Tariff Board relied on two scientific publications that were not put into evidence or referred to at the hearing. The Supreme Court found this to be a breach of the rules of natural justice. Pigeon J. noted, at para. 18: “It is clearly contrary to those rules to rely on information obtained after the hearing was completed without disclosing it to the parties and giving them an opportunity to meet it.” He added at para. 19 that this was a “grave error”. In my view this principle applies to this case. See also Cronk v. Canadian General Insurance Co. (1995) 1995 CanLII 814 (ON CA), 25 O.R. (3d) 505, at paras. 24-26, per Lacourciere J.A.. R. v. G.F
In R. v. G.F (SCC, 2021) the Supreme Court of Canada cited R v Mian (SCC, 2014) as a leading case on natural justice:
.... It argues that this was a breach of natural justice, in contravention of this Court’s decision in R. v. Mian, 2014 SCC 54,  2 S.C.R. 689.. McGregor v. Pitawanakwat
 While this point is moot as I have determined that the Court of Appeal erred in reaching its conclusion, I do not agree that Mian was breached. Mian sought to strike a balance between the adversarial process and the appellate court’s duty to ensure that justice is done. In pursuit of that duty, sometimes the appellate court will need to raise a new issue that suggests error in the decision below that goes beyond the arguments set forth by the parties. If the appellate court raises a new issue, fairness to the adversarial process requires the court to provide the parties with notice and an opportunity to respond to it: Mian, at para. 30. However, where the appellate court raises an issue that is not “new” but rather is rooted in or forms a component of the issues raised by the parties, Mian gives appellate courts a discretion to determine whether notice and submissions are warranted: para. 33.
In McGregor v. Pitawanakwat (Ont CA, 2017) the court noted the useful point that a violation of natural justice in a hearing is appealable regardless of whether the violation influenced the outcome:
 A final preliminary point is that the denial of a fair hearing is a free-standing ground of review. A correct decision cannot cure an unfair hearing, because the unfairness would taint the entire proceedings: see R. v. S. (R.D.), 1997 CanLII 324 (SCC),  3 S.C.R. 484, at para. 100.