CG52706 | Company reconstructions: shareholder: cancellation or extinction of shares

From HM Revenue & Customs · Capital Gains Manual

There is no need for the original shares to be cancelled, or otherwise extinguished. In many cases the shares will have become worthless and may be cancelled or disposed of for a nominal amount. However, in the case of a demerger, see CG52725, and similar examples the shareholders will retain their original shares.