(b) A person authorised under this subsection is not entitled to exercise the power referred to unless he or she is in uniform and has received (whether before or after the commencement of this Act) training and instruction which in the opinion of the person or if he or she is authorised by another, the person authorising him or her, after consultation with the Garda Síochána, is such as will provide guidance to him or her in the exercise of that power.