Change in rate of tax determines time of supply based on invoice date or payment receipt, with specified permutations. Change in the rate of tax determines the time of supply by reference to invoice issue and receipt of payment, with different rules where supply occurred before or after the rate change. If supply was before the change, time of supply is set by combinations of invoice date and payment date as specified; if supply was after the change, analogous permutations decide the time of supply. The date of receipt of payment is the earlier of book entry or bank credit, and bank credit after four working days from the rate change is treated as the date of receipt.