15.—(1) For the purposes of regulation 14 where the circumstances giving rise to the alteration are the coming into existence of an advertising hereditament those circumstances shall be treated as occurring when —
(a)any structure or sign is erected, after the right constituting the hereditament has been let out or reserved, to enable the right to be exercised; or
(b)any advertisement is exhibited in pursuance of the right,
whichever is earlier; and such a hereditament shall be treated for the purposes of Part 3 of the Act as coming into occupation at that time.
(2) The erection, dismantling or alteration of any structure or sign for enabling the advertising right to be exercised, after the time mentioned in paragraph (1), shall be treated for the purposes of a proposal made on the grounds set out in regulation 4(1)(b) as a material change of circumstances.
(3) In this regulation —
“advertising hereditament” means a hereditament consisting of a right to which section 64(2) of the Act applies;
“advertising right” means a right which is such a hereditament; and
“structure” includes a hoarding, frame, post or wall.