6. Regulation 3 shall not apply where the planning authority to which the application is made is satisfied–
(a)that the application relates solely to the use of a building or other land for a purpose of any class specified in the Schedule to the Town and Country Planning (Use Classes) (Scotland) Order 1997(1);
(b)that the existing use of that building or other land is for another purpose of the same class; and
(c)that the making of an application for planning permission in respect of the use to which the application relates is necessary by reason of and only by reason of a condition imposed on a permission granted or deemed to be granted under Part III of the 1997 Act.
SI 1997/3061 as amended by SI 1998/1196.