Retrospective amendment to CENVAT credit rules permits option to pay attributable input credit with interest upon application. Persons may opt to follow the retrospective amendment to rule 6 by paying the prescribed amount with interest and applying to the Commissioner of Central Excise within six months of assent, providing documentary evidence and a Chartered Accountant or Cost Accountant certificate quantifying input credit attributable to inputs or input services used in or in relation to the manufacture of exempted goods. The Commissioner shall verify payment within two months and require any differential payment with interest, payable within ten days of notice.