Modvat credit use restricted: cannot be applied to Special Excise duty before the notification's effective date. Clarification that Modvat credit of specified duties may not be utilised for payment of Special Excise duty for the period before Notification No. 138/88 C.E. became operative; the notification is effective from 8 4 1988, so credit utilisation for the interval prior to that date is not permitted and cases should be decided accordingly.