The Driving & Vehicle Licensing Agency (DVLA) is the UK governmental body which oversees the database of all the driving licences registered in the country, additionally they oversee all vehicle tax collection and registration across Great Britain. You should call their vehicle enquiries helpline 0300 790 6802 to get your vehicle tax and to notify them that you have over-paid in order to get a refund. By contrast you can also call this helpline if you would like to register your vehicle as off-the-road by making a Statutory Off Road Notification (SORN), meaning you no longer have to pay tax on that car. This is also the main contact number for vehicle registration, therefore if you would like to place a personalised number plate on your car you must phone the DVLA in order to legally update your registration. Similarly if you need a new log book (V5C certificate) for your vehicle you can call them in order to get a replacement sent out to you.