In section 12 (calculation of amount to be requisitioned by regional water boards), in subsection (2)(b) for the words between " ' relevant financial year' " and " authority, and " there shall be substituted the words " means, in the case of a requisition in respect of the financial year 1975-76, that year, and, in the case of a requisition in respect of any subsequent financial year, the financial year in respect of which the requisition is made or, if the water authority and the contributing authority agree, the financial year of the contributing authority immediately preceding the year in respect of which the requisition is made on the ".