419Term of detention in a detention centre
(1)The term for which a person may be detained in a detention centre shall not exceed three months at a time; and accordingly no court may pronounce an order the effect of which would be that a person would be liable to be detained for more than that period.
(2)Where a court has before it a person convicted of an offence punishable with imprisonment who is serving a sentence of detention in a detention centre or who has been sentenced to and has not yet started to serve such a sentence as aforesaid, it may pass either of the following sentences (subject to the requirements of any enactment relating to those sentences)—
(a)a sentence of detention in a young offenders institution, or, if the person is of or over 21 years of age, a sentence of imprisonment, for a period not exceeding the aggregate of the unexpired portion of the sentence of detention in a detention centre and the maximum period of detention in a young offenders institution or of imprisonment, as the case may be, which the court may impose for the offence of which it has convicted the person ; or
(b)a sentence of Borstal training;
and in that event the sentence of detention in a detention centre shall cease to have effect.