Criminal - Certiorari. R. v. M.N.
In R. v. M.N. (Ont CA, 2022) the Court of Appeal considers the rare criminal use of certiorari:
 Certiorari is an extraordinary remedy, the use of which is “tightly limited” by the Criminal Code and the common law to ensure that the general prohibition against interlocutory appeals in criminal matters is respected: R. v. Awashish, 2018 SCC 45,  3 S.C.R. 87, at para. 10. This general prohibition is a well-established principle of our criminal justice system that helps ensure the timely resolution of criminal matters: Mills v. The Queen, 1986 CanLII 17 (SCC),  1 S.C.R. 863, at p. 959; R. v. Meltzer, 1989 CanLII 68 (SCC),  1 S.C.R. 1764, at p. 1774; Dagenais v. Canadian Broadcasting Corp., 1994 CanLII 39 (SCC),  3 S.C.R. 835, at p. 857.
 Expanding the availability of extraordinary remedies to effect an “end-run” around this general prohibition would undermine the principles espoused by the Supreme Court of Canada in R. v. Jordan, 2016 SCC 27,  1 S.C.R. 631, as interlocutory appeals threaten the timely delivery of justice by fragmenting criminal trials: Awashish, at para. 10. As the Supreme Court of Canada explained in Awashish, challenging interlocutory rulings in criminal matters “risks having issues decided without the benefit of a full evidentiary record – a significant source of delay and an inefficient use of judicial resources”: para. 10.
 It is in part for this reason that certiorari is only available to parties in a criminal matter where a judge of the provincial court makes a jurisdictional error: Awashish, at para. 20. That is, an error where the judge “fails to observe a mandatory provision of a statute” or “acts in breach of the principles of natural justice”: Awashish, at para. 23. As this court explained in York (Regional Municipality) v. McGuigan, 2018 ONCA 1062, 144 O.R. (3d) 81, at para. 64:
Certiorari is an extraordinary remedy, which issues from the superior court to ensure that courts of limited authority, such as the provincial offences court, do not exceed their limited jurisdiction. Provided courts of limited jurisdiction do not exceed the scope of their authority, certiorari is not available to the parties to a proceeding to control the manner in which the authority is exercised. Certiorari is only available when the alleged error goes to the jurisdiction of the provincial court itself. It is not enough to identify an alleged legal error in the provincial court’s interlocutory ruling. Any such error would properly be dealt with at the conclusion of the trial: R. v. Stipo, 2019 ONCA 3, 144 O.R. (3d) 145, at para. 52, and R. v. Amiri, 2021 ONCA 902.
 Finally, it must be remembered that certiorari has always been understood to be a discretionary remedy of last resort. Accordingly, it would have been “incumbent upon the applicant to establish that the circumstances are such that the interests of justice necessitate the immediate granting of the prerogative or Charter … remedy by the Superior Court”: R. v. Duvivier (1991), 1991 CanLII 7174 (ON CA), 3 O.R. (3d) 49 (Ont. C.A.), at pp. 53-54, per Doherty J.A.; and see McGuigan, at para. 48.