If the first buyer is entitled under any enactment to an exemption from tax which, apart from this subsection, would extend to the interest, then the exemption shall not extend to an amount equal to the appropriate amount in respect of the interest, as determined in accordance with section 735.

If the first buyer is so entitled and any annual payment is payable by him out of the interest, the annual payment shall be deemed as to the whole thereof to be paid out of profits or gains not brought into charge to income tax, and section 349(1) shall apply accordingly.