Sch 2A para 15
A power conferred by this Schedule to require a person to attend a police station for the purposes of taking fingerprints , a sample or a photograph under any provision of this Act may be exercised only in a case where the fingerprints , sample or photograph may be taken from the person under that provision (and, in particular, if any necessary authorisation for taking the fingerprints , sample or photograph under that provision has been obtained).