11.—(1) In the case of an existing process, the prescribed date is, subject to paragraph 13,—
(i)in a case falling within paragraph (2), the date at which the change mentioned in that paragraph is made;
(ii)where sub-paragraph (i) does not apply, the day after that on which the period for applying for authorisation in accordance with the Table in paragraph 12 expires.
(2) A case falls within this paragraph if the person carrying on the process makes a substantial change in the process in the period specified in paragraph 12 in relation to the description of processes which comprise that process (when changed) and that change—
(i)has not occasioned construction work which is in progress at the beginning of that period; or
(ii)is not the subject of a contract for construction work entered into before the beginning of that period.