Extension of return filing period allows withdrawal of assessment order upon late filing with daily late fee; interest liability persists. The amendment lengthens the period to furnish a valid return after service of an assessment order from thirty days to sixty days and permits a further sixty day extension on payment of an additional late fee of one hundred rupees per day for delay beyond the initial sixty days; if a valid return is filed within that extended period and the additional late fee paid, the assessment order is deemed to have been withdrawn while liability to pay interest under section 50(1) and late fee under section 47 continues.