An appeal under section 222 above may be brought out of time with the consent of the Board or the Special Commissioners; and the Board—
(a)shall give that consent if satisfied, on an application for the purpose, that there was a reasonable excuse for not bringing the appeal within the time limited and that the application was made thereafter without unreasonable delay, and
(b)shall, if not so satisfied, refer the application for determination by the Special Commissioners.