R (London Borough of Harrow) v Maidstone Crown Court  EWHC Admin 385
A Crown Court judge’s purported finding that a defendant was not guilty by reason of insanity was outside his jurisdiction and so not pursuant to the indictment, and so could be challenged by judicial review. [MHLR.]
The summary below has been supplied by Kris Gledhill, Editor of the Mental Health Law Reports. The full report can be purchased from Southside Online Publishing (if there is a "file not found" error, it means this particular report is not yet available online). More similar case summaries from the year 1999 are available here: MHLR 1999.
Insanity – amenability to challenge of finding of Not Guilty by Reason of Insanity without a jury - R v Maidstone Crown Court ex p LB Harrow  MHLR 84
Points Arising: A Crown Court judge’s purported finding that a defendant was not guilty by reason of insanity was outside his jurisdiction and so not pursuant to the indictment, and so could be challenged by judicial review.
Facts and Outcome: HW appeared at the Crown Court on a charge of arson; the judge purported to accept a plea of Not Guilty by Reason of Insanity, based on the unanimous medical evidence available, without empanelling a jury, and then made a supervision order under s5 Criminal Procedure (Insanity) Act 1964 with a condition of treatment by a named doctor; the order was later reissued administratively to identify LB Harrow social services as the named supervisor (rather than the probation service). On an application to challenge the order as ultra vires because the statutory regime required a jury verdict, the question arose as to whether the matter related to trial on indictment as so was outside the scope of judicial review (s29 Supreme Court Act 1981). The Divisional Court held that the Crown Court judge had acted outside jurisdiction, purportedly but not actually pursuant to indictment, and so was amenable to judicial review; and in any event the involvement of LB Harrow was pursuant to a revised order not made by a Crown Court judge and so amenable to judicial review. The order was quashed and the matter remitted to the Crown Court.
Old wiki notes
A plea of not guilty by reason of insanity (providing the accused is fit to plead and be tried) must be followed by the trial of that issue by a jury; the judge was wrong to enter a verdict without taking the verdict of a jury; the High Court had jurisdiction to review the order even though it was a matter relating to trial on indictment; case remitted to Crown Court.
Possible Bailii link (not there when checked last night, but might have appeared since)