This section applies where—
on the summary trial of a specified offence (see section 306) a person aged under 18 is convicted of the offence, and
the court is of the opinion that an extended sentence of detention under section 254 would be available in relation to the offence.
The court must commit the offender in custody or on bail to the Crown Court for sentence in accordance with section 22(2).
For powers of the court, where it commits a person under subsection (2), also to commit in respect of other offences, see section 20.
Nothing in this section prevents the court from committing a person convicted of a specified offence to the Crown Court for sentence under section 16 , 16A or 19 if the provisions of that section are satisfied.