Appellant limited to grounds of appeal

15. On the hearing of an appeal or application against a determination or assessment the appellant or applicant shall not be entitled to rely upon any grounds not stated in his notice of reference or statement of case or application unless the President or the Tribunal thinks it just in all the circumstances, and on such terms as to costs or adjournment or otherwise as he or it may think fit, to allow such additional grounds to be put forward as may appear to the President or the Tribunal to be material.