3E+WA local authority shall for every period of six months declare, on a date falling within the month immediately preceding that period—
(a)a rate applicable to the advances and transfers mentioned in section 438(1)(a) and (c) (advances under section 435 and transfers of mortgages under section 442), and
(b)a rate applicable to sums left outstanding as mentioned in section 438(1)(b) (sums left outstanding on disposal of house).