A person in whose case there is returned a verdict of not guilty by reason of insanity may appeal to the Court of Appeal against the verdict—
(a)on any ground of appeal which involves a question of law alone; and
(b)with the leave of the Court of Appeal, on any ground which involves a question of fact alone, or a question of mixed law and fact, or on any other ground which appears to the Court of Appeal to be a sufficient ground of appeal;
but if the judge of the court of trial grants a certificate that the case is fit for appeal on a ground which involves a question of fact, or a question of mixed law and fact, an appeal lies under this section without the leave of the Court of Appeal.