The following subsection shall be added at the end of section 9 of the Increase Act (gratuities and lump sums)—

“(9)

In any case where—

(a)

a lump sum beginning after the coming into force of this subsection, or an instalment of such a lump sum, is paid, but

(b)

the amount of that lump sum or instalment is subsequently recalculated, and

(c)

in consequence of the recalculation, an additional amount becomes payable by way of lump sum,

the additional amount shall not be increased under this Part of this Act in respect of the whole or any part of the period beginning with the day on which the lump sum or instalment became payable and ending with the day on which the additional amount is paid.”