About changing owner or title holder particulars for a vehicle
Any changes to the particulars of the vehicle owner or title holder must be communicated to the appropriate registering authority within 21 days after such change. Use the notification of change of address or particulars of person or organisation (NCP) form.
When you sell your vehicle, you must notify your registering authority on the Notification of change of ownership/Sale of motor vehicle (NCO) form. The new owner must register the car in their name.