CG51890 - Share reorganisations: apportionment of cost: general
The normal part disposal formula in TCGA92/S42 does not apply to the apportionment of the cost of shares in a new holding. Instead you must use the formulae set out in TCGA92/S129 and TCGA92/S130. In practice there is unlikely to be much difference between an apportionment using Section 42 and an apportionment using Sections 129 and 130. Indeed in many cases the figures will be exactly the same. The crucial feature of Sections 129 and 130 is not the method of apportionment but the time at which you make the apportionment.
The main rule in TCGA92/S129 is that you make the apportionment at the date of disposal of any of the shares in the new holding. The instructions on Section 129 are at CG51892+. However, Section 129 does not apply if the new holding includes more than one class of share or debenture and any of the shares or debentures are quoted. In this case you make the apportionment at the date of the reorganisation, TCGA92/S130. The instructions on Section 130 are at CG51965+.