4(1)On the occurrence of a chargeable event in relation to any relevant shares in relation to which there has not been a previous chargeable event—
(a)a chargeable gain shall be treated as accruing at the time of the event; and
(b)the amount of the gain shall be equal to so much of the original gain as is an amount against which there has under this Schedule been set any expenditure on those shares.
(2)In determining for the purposes of this Schedule any question whether any shares to which a chargeable event relates are shares the expenditure on which has under this Schedule been set against the whole or any part of any gain, the assumptions in sub-paragraph (3) below shall apply and, in a case where the shares are not (within the meaning of section 151B) eligible for relief under section 151A(1), shall apply notwithstanding anything in any of sections 104, 105 and 107.
(3)Those assumptions are that—
(a)as between shares acquired by the same person on different days, those acquired on an earlier day are disposed of by that person before those acquired on a later day; and
(b)as between shares in a company that were acquired on the same day, those the expenditure on which has been set under this Schedule against the whole or any part of any gain are disposed of by that person only after he has disposed of any other shares in that company that were acquired by him on that day.
(4)Where at the time of a chargeable event any relevant shares are treated for the purposes of this Act as represented by assets which consist of or include assets other than the relevant shares—
(a)the expenditure on those shares which was set against the gain in question shall be treated, in determining for the purposes of this paragraph the amount of expenditure on each of those assets which is to be treated as having been set against that gain, as apportioned in such manner as may be just and reasonable between those assets; and
(b)as between different assets treated as representing the same relevant shares, the assumptions mentioned in sub-paragraph (3) above shall apply with the necessary modifications in relation to those assets as they would apply in relation to the shares.