18. A scheme made by a joint board under this Part shall provide—
(a)that each constituent council shall notify the joint board before the beginning of the year to which the scheme relates of the amount, if any, which the council has allocated towards payment of special responsibility allowances for that year under the scheme;
(b)that any special responsibility allowance payable under the scheme in relation to any year shall be paid by each constituent council in the proportion which the amount, if any, for that year which that council has notified to the joint board under paragraph (a) bears to the aggregate amount for that year which all the constituent councils have notified to the joint board in accordance with that paragraph; and
(c)that payments of special responsibility allowances are to be made at such times as may be specified in the scheme.