16. Power to order detention.

Until a day to be appointed1, where a person aged at least 18 but under 212 is convicted of an offence which is punishable with imprisonment in the case of a person aged 21 or over3, the court4 must pass a sentence of detention in a young offender institution5 if it is of the opinion:

  1.  

    (1)     that the offence, or a combination of the offence and one or more offences associated6 with it, was so serious that only such a sentence could be justified for it