The RUC-Licence (RUC)
Owners of diesel-vehicles also have to pay Road User Charges. There is a sticker at the left-bottom corner of the wind screen telling you at what odometer reading it expires. When buying a car make sure the km on the odometer are less than the km on the sticker. You can buy more km at any post office. Do it before the old one expires!
Links for more information on RUC-Licence: