s 252 Maximum sentence
(1) This section applies where the court imposes a sentence of detention under section 250 by virtue of— (a) section 251, or (b) section 311 (minimum sentence for certain offences involving firearms that are prohibited weapons). (2) The period of detention specified in the sentence must not exceed— (a) the maximum term of imprisonment with which the offence is punishable in the case of a person aged 21 or over, or (b) life, if the offence is punishable with imprisonment for life in the case of a person aged 21 or over.