An appellant, notwithstanding that he is in custody, shall be entitled to be present if he desires it, on the hearing of his appeal, except where the appeal is on some ground involving a question of law alone, but, in that case and on an application for leave to appeal and on any proceedings preliminary or incidental to an appeal, shall not be entitled to be present, except where it is provided by Act of Adjournal that he shall have the right to be present, or where the High Court gives him leave to be present