[In every case of an offence punishable with imprisonment as well as fine, in which the offender is sentenced to a fine, whether with or without imprisonment, and in every case of an offence punishable 4[with imprisonment or fine, or] with fine only, in which the offender is sentenced to a fine.] it shall be competent to the Court which sentences such offender to direct by the sentence that, in default of payment of the fine, the offender shall suffer imprisonment for a certain term, which imprisonment shall be in excess of any other imprisonment to which he may have been sentenced or to which he may be liable under a commutation of a sentence.