8.The rateable value is a notional annual rental value attributed to a property on the basis of certain assumptions. The valuer is required to determine the annual amount of rent which, if the property were vacant and available for letting on the open market, it would attract for a tenancy from year to year. The tenancy is a notional, or hypothetical one, not based on the actual characteristics of  the landlord or the tenant (if there are a landlord and a tenant) or the terms of any tenancy to which the property may be subject.
9.The physical characteristics of the property, and its surroundings, which are taken into account in the valuation are, for the most part,  those which are assumed to be attributable to the property on the day on which the list comes into force or, if there is a subsequent change of circumstances, on a day determined in accordance with regulations made by the Secretary of State.
10.The rental levels to be considered for the purposes of estimating rateable values, whether on the list first coming into force or in relation to its subsequent alteration, are however those applicable by reference to a day falling two years before the day on which the lists in question come into force (the ‘antecedent valuation date’). Thus unless there is a subsequent change of circumstances, the value attributed to a property on the day on which a list comes into force will apply for the calculation of each year’s rates bill for that property until the next list comes into force five years later.
Background The hypothetical tenancy