enabling a company to elect that, with respect to disposals after 31st March 1982, each of its holdings of certain securities of the same class which are held by it solely and beneficially and which have been so held for the length of time referred to in that Schedule shall be regarded for the purposes of the M1Capital Gains Tax Act 1979 as constituting a single asset; and

computing the indexation allowance applicable on a disposal of such a single asset.