Retroactive merger liability requires inter-company supplies to be included in turnover and taxed, with separate registrations maintained until order. When companies are amalgamated or merged with retrospective effect, transactions of supply between the constituent companies from the retrospective effective date until the date of the order are to be included in each company's turnover and are liable to tax. Notwithstanding the amalgamation order, the constituent companies are treated as distinct persons for the period up to the order date, and their registration certificates are cancelled with effect from the date of that order.