For the purposes of section 261B "the maximum amount" is the amount on which the person would be chargeable to capital gains tax for the year of assessment if—
the provisions mentioned below were ignored, and
no account were taken of the event mentioned below.
The provisions are—
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
section 1K(1) (annual exempt amount), and
section 261B.
The event is any event—
which occurs after the date on which the relevant amount (see section 261B(3)) can no longer be varied by the tribunal on appeal or on the order of a court, and
in consequence of which the amount chargeable to capital gains tax is reduced as a result of an enactment relating to capital gains tax.