20. Exercise of powers to be subject to sanction.
Save as otherwise provided in this Act, the exercise of any power or the performance of any duty conferred or imposed upon the Council by or under this Act which will involve expenditure, shall be subject to the following conditions, namely:
(a) that such expenditure, in so far as it is to be incurred in the year in which such power is exercised or duty performed, shall be provided for under a current budget-grant; and
(b) that if the exercise of such powers or the performance of such duty involves or is likely to involve expenditure for any period or at any time after the close of the said year, such expenditure shall not be incurred without the sanction of the Council.