A magistrates' court that has power to commit to prison a person convicted of an offence, or would have that power but for section 82 or 88 above, may order him to be detained within the precincts of the court-house or at any police station until such hour, not later than 8 o'clock in the evening of the day on which the order is made, as the court may direct, and, if it does so, shall not, where it has power to commit him to prison, exercise that power.
A court shall not make such an order under this section as will deprive the offender of a reasonable opportunity of returning to his abode on the day of the order.
This section shall have effect in relation to a person aged 18 or over but less than 21 as if references in it to prison were references to detention under section 108 of the Powers of Criminal Courts (Sentencing) Act 2000 (detention of persons aged 18 to 20 for default).