In any case submitted under section 366, the High Court—

   (a)  may confirm the sentence, or pass any other sentence warranted by law, or

   (b)  may annul the conviction, and convict the accused of any offence of which the Court of Session might have convicted him, or order a new trial on the same or an amended charge, or

   (c)  may acquit the accused person:

   Provided that no order of confirmation shall be made under this section until the period allowed for preferring an appeal has expired, or, if an appeal is presented within such period, until such appeal is disposed of.