Rating and Valuation (Miscellaneous Provisions) Act 1955

2 If, by reason of any structural alteration or other event occurring in the case of a hereditament after the beginning of the last year of the old list, an alteration has been made (whether before or after the passing of this Act) in the valuation list in force in that year with respect to the rateable value of the hereditament, then, for the purposes of paragraph (a) of subsection (2) of the principal section, and for the purposes of the following provisions of this Schedule, any reference to the total amount of rates (including any special rates) which were charged or would have been chargeable in respect of the hereditament for that year, or for any part of that year, shall be construed as a reference to the total amount of such rates which would have been chargeable if the rateable value as so altered had been shown in the valuation list as from the beginning of that year.