14(1)For the purposes of this Part, material development shall be taken to be begun on the earliest date on which any specified operation comprised in the material development is begun.
(2)In this paragraph “specified operation” means any of the following, that is to say—
(a)any work of construction in the course of the erection of a building;
(b)the digging of a trench which is to contain the foundations, or part of the foundations, of a building;
(c)the laying of any underground main or pipe to the foundations, or part of the foundations, of a building or to any such trench as is mentioned in (b) above;
(d)any operation in the course of laying out or constructing a road or part of a road;
(e)any change in the use of any land.
(3)Subject to sub-paragraph (4) below, material development shall for the purposes of this Part of this Schedule not be treated as carried out after a particular date if it was begun on or before that date.
(4)If, in the case of any land—
(a)material development thereof was begun on or before 17th December 1973 but was not completed on or before that date, and
(b)the development was on that date to any extent not authorised by planning permission (within the meaning of paragraph 10(3) above) then in force,
then, for the purposes of this Part of this Schedule, so much of the development carried out after that date as was not so authorised on that date shall be treated as begun on the earliest date after 17th December 1973 on which any specified operation comprised therein is begun, and shall accordingly be treated as material development of the land carried out after 17th December 1973.