Scale charges are a way of simply apportioning the private use of fuel in cars provided by VAT registered persons to themselves or their employees.
Output tax must be accounted for when VAT has been recovered in full on fuel paid for by the VAT registered person but some of that fuel is used privately (eg. journeys to and from a persons place of work). The fuel scale charge is a fixed output VAT charge which is based on the emissions of a car and is designed to cover the supply arising from the business providing and funding road fuel for private use in cars. The amount of VAT to be accounted for on the fuel scale charge is added to the output tax of the relevant VAT return.
VAT registered persons do not have to use the fuel scale charge. For example, they may keep detailed mileage records to separate business and private journeys and only recover VAT on the business element.