G.1—(1) Subject to sub-paragraphs (2) and (3), development is permitted by Class G subject to the prior approval of the mineral planning authority(1) of detailed proposals for the siting, design and external appearance of the building, plant or machinery proposed to be erected, installed, extended or altered.
(2) The prior approval referred to in sub-paragraph (1) is not required if—
(a)the external appearance of the mine or disused mine at or adjacent to which the development is to be carried out would not be materially affected;
(b)no building, plant or machinery, structure or erection—
(i)would exceed a height of 15 metres above ground level; or
(ii)where any building, plant, machinery, structure or erection is rearranged, replaced or repaired, would exceed a height of 15 metres above ground level or the height of what was rearranged, replaced or repaired, whichever is the greater, and
(c)the development consists of the extension, alteration or replacement of an existing building, within the limits set out in sub-paragraph (4).
(3) The prior approval referred to in sub-paragraph (1) may not be refused or granted subject to conditions unless the authority are satisfied that it is expedient to do so because—
(a)the proposed development would injure the amenity of the neighbourhood and modifications could reasonably be made or conditions reasonably imposed in order to avoid or reduce that injury; or
(b)the proposed development ought to be, and could reasonably be, sited elsewhere.
(4) The limits referred to in paragraph G.1(2)(c) are—
(a)that the cubic content of the building as extended, altered or replaced does not exceed that of the existing building by more than 25%; and
(b)that the floor space of the building as extended, altered or replaced does not exceed that of the existing building by more than 1,000 square metres.
See section 1(4) of the Act.