(1) If an offender has been sentenced to several terms of imprisonment in respect of any of which a non-parole period was fixed, the offender must serve—
(a) firstly, any term or terms in respect of which a non-parole period was not fixed;
(b) secondly, the non-parole period;
(c) thirdly, unless and until released on parole, the balance of the term or terms after the end of the non-parole period.
(2) If during the service of a sentence a further sentence is imposed, service of the first-mentioned sentence must, if necessary, be suspended in order that the sentences may be served in the order referred to in subsection (1).