(a) Subject to paragraph (b), where a court by or before which a person is convicted of an offence, not being an offence the sentence for which is fixed by law, is of opinion that after duly considering any report made under section 3A and having regard to the circumstances, , including the nature of the offence and the character, antecedents, age, , health, mental condition and home surroundings of the offender, it is expedient to do so, the court may, instead of sentencing him, make a probation order.