Time of supply rules link invoice date and payment receipt to determine taxable moment after a change in tax rate. Change in rate of tax determines the time of supply by reference to invoice date and date of receipt of payment: for supplies before the rate change, time of supply is the earlier of payment or invoice when both occur after the change, otherwise the invoice date if issued before or the payment date if received before; for supplies after the change, time of supply depends on the sequence of invoice and payment with analogous rules. Bank credit more than four working days after the change is treated as the date of receipt; 'date of receipt' means the earlier of book entry or bank credit.