Subject to the provisions of subsection (2) below, where the Treasury are satisfied with respect to any class of persons in receipt of any salary, fees or emoluments payable out of the public revenue that such persons are obliged to lay out and expend money wholly, exclusively and necessarily in the performance of the duties in respect of which such salary, fees or emoluments are payable, the Treasury may fix such sum as in the opinion of the Treasury represents a fair equivalent of the average annual amount laid out and so expended by persons of that class, and in charging income tax on that salary or those fees or emoluments there shall be deducted from the amount thereof the sums so fixed by the Treasury.

If any such person would, but for the provisions of subsection (1) above, be entitled to deduct a larger amount than the sum so fixed, that amount may be deducted instead of the sum so fixed.