Subject to any provision to the contrary, if on the disposal of an asset there is an unindexed gain, an allowance ("the indexation allowance") shall be allowed against the unindexed gain—
and any reference in this Act to an indexation allowance or to the making of an indexation allowance shall be construed accordingly.
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Indexation allowance is not allowed in respect of changes shown by the retail prices indices for months after December 2017.
For the purposes of this Chapter, in relation to any disposal of an asset—
Notwithstanding anything in section 16 of this Act, this section shall not apply to a disposal on which a loss accrues.
In determining what sum (if any) was taken into account as mentioned in subsection (2)(b) above, account shall be taken of any provision of any enactment which, for the purpose of the computation of the gain, increases, excludes or reduces the whole or any part of any item of expenditure falling within section 38 or provides for it to be written-down.
Sections 54 and 108 and this section have effect subject to sections 56, 57, 109, 110 ... , 113, 131 and 145.