Computing the amount to assess: business changes: succession and changes in ownership: date of succession
Where a business is transferred as a going concern the date of succession is usually the date provided in the sale agreement for the completion of the transfer or, in the absence of such a date, the date of the agreement. However there may be evidence that the purchaser in fact took possession of the business at an earlier date, in which case that earlier date is the date of succession (see Todd v Jones Brothers Ltd  15TC396, where there was no such evidence, and Angel v Hollingworth & Co  37TC714, for evidence accepted by the Commissioners as sufficient).
The date of succession as determined will be the date of cessation for the predecessor and the date of commencement for the successor.
The date at which a trade is transferred is also relevant for companies in the context of S941 Corporation Tax Act 2010, which modifies the normal cessation and commencement rules where a trade is transferred between companies in common ownership. See CTM06010.