In any case where—
an option is exercised; and
the nature of the option (or its exercise) is such that the grantor of the option is liable to make, and the person exercising it is entitled to receive, a payment in full settlement of all obligations under the option,
subsections (2) and (3) below shall apply in place of subsections (2) and (3) of section 144.
As regards the grantor of the option—
he shall be treated as having disposed of an asset (namely, his liability to make the payment) and the payment made by him shall be treated as incidental costs to him of making the disposal; and
the grant of the option and the disposal shall be treated as a single transaction and the consideration for the option shall be treated as the consideration for the disposal.
As regards the person exercising the option—
he shall be treated as having disposed of an asset (namely, his entitlement to receive the payment) and the payment received by him shall be treated as the consideration for the disposal;
the acquisition of the option (whether directly from the grantor or not) and the disposal shall be treated as a single transaction and the cost of acquiring the option shall be treated as expenditure allowable as a deduction under section 38(1)(a) from the consideration for the disposal; and
for the purpose of computing the indexation allowance (if any) on the disposal, the cost of the option shall be treated (notwithstanding paragraph (b) above) as incurred when the option was acquired.
In any case where subsections (2) and (3) above would apply as mentioned in subsection (1) above if the reference in that subsection to full settlement included a reference to partial settlement, those subsections and subsections (2) and (3) of section 144 shall both apply but with the following modifications—
for any reference to the grant or acquisition of the option there shall be substituted a reference to the grant or acquisition of so much of the option as relates to the making and receipt of the payment or, as the case may be, the sale or purchase by the grantor; and
for any reference to the consideration for, or the cost of or of acquiring, the option there shall be substituted a reference to the appropriate proportion of that consideration or cost.
In this section "appropriate proportion" means such proportion as may be just and reasonable in all the circumstances.