(1)  Subject to sections 15 and 16 , a sentence of imprisonment commences on the day on which it is imposed unless the offender is not then in custody.

(2)  If the offender is not then in custody, the sentence of imprisonment commences on the day on which the offender is apprehended under a warrant to imprison issued in respect of the sentence.

(3)  If an offender who is sentenced to a term of imprisonment is allowed to be or go at large for any reason, the period between then and the day on which the offender is taken into custody to undergo the sentence does not count in calculating the term to be served and service of the sentence is suspended during that period.

(4)  If an offender who is lawfully imprisoned under a sentence escapes or fails to return after an authorised absence, the period between then and the day on which the offender surrenders or is apprehended does not count in calculating the term to be served and service of the sentence is suspended during that period.

(5)  Despite anything to the contrary in this Act or any other enactment or in any rule of law or practice, a sentence of imprisonment is to be calculated exclusive of any time during which service of it is suspended under subsection (3) or (4) .

(6)  If an offender to whom subsection (4) applies is, in the period during which service of the sentence is suspended under that subsection, imprisoned under another sentence, the unexpired portion of the suspended sentence takes effect –

(a) if it is to be served cumulatively on the sentence the offender is then undergoing, on the day that sentence is completed; or

(b) in any other case, at the end of the period of suspension.

(7)  If an offender who is sentenced to a term of imprisonment and allowed to be or go at large pending an appeal or the consideration of any question of law reserved or case stated is imprisoned under another sentence at the time when the appeal, question of law reserved or case stated is finally determined, the first-mentioned sentence or the unexpired portion of it takes effect –

(a) if it is to be served cumulatively on the sentence the offender is then undergoing, on the day that sentence is completed; or

(b) in any other case, on the day the appeal, question of law reserved or case stated is finally determined.

(8)  Subsection (7) applies unless the sentencing court or the court determining the appeal, question of law or case stated otherwise directs.