Section sixty-six of the principal Act is amended in subsection (1) by the deletion of the words" at the rate of three per C centum" and the substitution therefore of " at the rate of two per, centum". The Third Schedule to the principal Act is amended in, paragraph 5 by the deletion of the proviso to sub-paragraph (1) and the substitution therefore of: (i) The amount of tax which would otherwise be payable by such person in that charge year is not reduced by more than twenty percentum as a resu