Paragraph 17 of the M1said Schedule 2 (modification of agreements made before 1st October 1970 where additional duty is payable under the Finance Act 1970 as compared with section 13 of the M2Finance Act 1966) shall have effect in relation to section 6 of this Act as if for references to 1st October 1970, the Finance Act 1970 and section 13 of the Finance Act 1966 there were substituted respectively references to 1st October 1980, the said section 6 and section 14 of the said Act of 1972.