Motor tax discs are vehicle specific, with the registration number printed on them to ensure that the disc relates only to a particular vehicle and to prevent the same tax disc being transferred to vehicles other than the one that has been taxed.
There would be administrative and cost impacts attaching to any system of returning motor tax discs upon sale of the vehicle and issuing a new tax disc with a new registration number. These impacts would increase if the tax class of the replacement vehicle was not the same as the original vehicle.
Upon sale of a vehicle, the motor tax status of the vehicle does not change, and the vehicle remains taxed until the validity of the existing tax disc expires. Accordingly, the value of the residual motor tax can be factored into the price it is traded for, and it is not clear that transfer of the tax disc to a different vehicle could have any significant net impact on the cost of trading one vehicle for another.
It is also open to the seller of a vehicle to manage their motor tax affairs to minimise the residual motor tax upon sale of the vehicle, including through the availability of quarterly or half yearly motor tax options.
Accordingly, I do not propose to make the suggested change.