9A. Interest on failure to pay tax or penalty. -

(a) If the amount of any tax payable under sections 4,4A or 6A is not paid in the manner provided in section 5 or 5A within the period allowed; or (b) if the amount specified in any notice of demand whether for tax or penalty or interest is not paid within the period specified in such notice or in the absence of such specifications within 30 days from the date of service of such notice; the proprietor shall be liable to pay simple interest on such amount at one and half per cent month from the day commencing after the end of the said period for a period of three months and at two percent per month thereafter during the time he continues to make default in such payment. Provided that where, as a result of any order by competent authority under this Act, the amount on which interest was payable under this section has been reduced, the interest shall be reduced accordingly and the excess interest paid, if any, shall be refunded.]