Interest on customs duty now subject to centrally fixed rates, payable from month after default; waiver for prompt voluntary payment. Substitution of the interest provision requires the person liable for unpaid, short-paid, short-levied or erroneously refunded customs duty to pay interest at rates fixed by the Central Government, calculated from the first day of the month after the duty ought to have been paid or from the date of an erroneous refund until payment, and includes interest on amounts already paid; a limited waiver exempts voluntary full payments made within a specified short period following Board direction if no appeal right is reserved, and the rule is not to apply to liabilities arising before assent to the Finance Bill, 2001.