3(1)Subject to the provisions of this Schedule, the annual rate of duty applicable to a goods vehicle which is a rigid goods vehicle and has a plated gross weight which exceeds 12 tonnes shall be determined in accordance with Table A in Part II of this Schedule by reference to—
(a)the plated gross weight of the vehicle; and
(b)the number of axles on the vehicle.
(2)If a rigid goods vehicle to which sub-paragraph (1) above applies is used for drawing a trailer which—
(a)has a plated gross weight exceeding 4 tonnes; and
(b)when so drawn, is used for the conveyance of goods or burden;
the annual rate of duty applicable to it in accordance with that sub-paragraph shall be increased by the amount of the supplement which, in accordance with Table B in Part II of this Schedule, is appropriate to the gross plated weight of the trailer being drawn.