Time of supply on change in tax rate governed by invoice and payment dates, with bank credit treated as receipt. Change in rate of tax fixes the time of supply by reference to invoice and payment dates. For supplies before the rate change, the time of supply is the earlier of invoice or payment when both follow the change; the invoice date if issued before but paid after; and the payment date if paid before but invoiced after. For supplies after the change, the time of supply is the payment date when payment follows but invoice preceded; the earlier of invoice or payment when both preceded; and the invoice date when invoiced after but paid before. Bank credit after four working days is treated as receipt of payment; receipt means book entry or bank credit, whichever is earlier.