(1)Where—
(a)a vehicle licence has been taken out for a vehicle at any rate of vehicle excise duty, and
(b)at any time while the licence is in force the vehicle is used so as to subject it to a higher rate,
duty at the higher rate becomes chargeable in respect of the licence for the vehicle.
(2)For the purposes of subsection (1) a vehicle is used so as to subject it to a higher rate if it is used in an altered condition, in a manner or for a purpose which—
(a)brings it within, or
(b)if it was used solely in that condition, in that manner or for that purpose, would bring it within,
a description of vehicle to which a higher rate of duty is applicable.
(3)For the purposes of subsection (1) a vehicle in respect of which a lower rate of duty is chargeable by virtue of regulations under paragraph 13 of Schedule 1 is also used so as to subject it to a higher rate if it is used in contravention of a condition imposed under or by virtue of sub-paragraph (2) of that paragraph.
(4)Where duty at a higher rate becomes chargeable under subsection (1) in respect of a vehicle licence, the licence may be exchanged for a new vehicle licence for the period—
(a)beginning with the date on which the higher rate of duty becomes chargeable, and
(b)ending with the period for which the original licence was issued.
(5)A new vehicle licence may be obtained under subsection (4) only on payment of the appropriate proportion of the difference between—
(a)the amount of duty payable on the original licence, and
(b)the amount of duty payable on a vehicle licence taken out for the period for which the original licence was issued but at the higher rate of duty.
(6)For the purposes of subsection (5)“the appropriate proportion” means the proportion which the number of months in the period—
(a)beginning with the date on which the higher rate of duty becomes chargeable, and
(b)ending with the period for which the original licence was issued,
bears to the number of months in the whole of the period for which the original licence was issued (any incomplete month being treated as a whole month).
(7)If the higher rate has been changed since the issue of the original licence, the amount under subsection (5)(b) is calculated as if that rate had been in force at all material times at the level at which it is in force when it becomes chargeable.