20. Where it appears to the funding authority that the amount of maintenance grant determined in respect of a school for the financial year in question is insufficient to enable the governing body of the school adequately to carry out their functions with respect to the conduct of the school, they may, after consultation with the local education authority and the governing body of the school, redetermine the amount of maintenance grant payable in respect of the school for the year and revise their determination by adding such amount as appears to them to be fair and reasonable for the purpose of enabling the governing body adequately to carry out their functions with respect to the conduct of the school.