18.—(1) This regulation applies in relation to the principal area if one or more special items relate to a part only of that area.
(2) The appropriate authority must calculate different basic amounts of council tax—
(a)for any part of the principal area to which no special items relate, and
(b)for any part of that area to which one or more special items relate.
(3) The amount calculated under paragraph (2) for each part of the principal area must be more than the uniform amount of council tax.