According to PACE (Police and Criminal Evidence Act 1984), if a person under the age of 17 or if a Police Officer suspects that a person (either juvenile or adult) being interviewed is vulnerable, then an appropriate adult is required. This assessment should be made by considering external information from the interviewee's General Practitioner, Carer or Social Worker. The interviewee may also provide information themselves about their vulnerability.

The Custody officer (who is usually a police sergeant) has a duty of care to any detainee exhibiting unusual behavior, to request an appropriate adult.

If unusual behavior at interview occurs, such as excessive anxiety or agitation, incoherent speech, failure to understand questions, the interviewing Officer should also consider requesting the attendance of an appropriate adult.

Appropriate Adults can be carer's, drawn from the voluntary sector, or professionally employed.

In all cases Appropriate Adults must be independent and have no involvement whatsoever in the incidents being investigated.

Professional Appropriate adults, and those who regularly volunteer, should have recently been checked through the Criminal Records Bureau. National guidelines suggest that for best practice all Appropriate Adults with in the voluntary or professional sectors should have had a minimum of eighteen and a half hours recognized training. Additionally two police station observations, one of which should have been a supervised case mentored by a trained Appropriate Adult.

Familiarity with PACE is a fundamental part of Appropriate Adult work. This is essential to ensure the detainee's welfare and rights are safeguarded during the detention, interview and release procedures. In addition Appropriate Adults dealing with vulnerable adult cases and mental health issues, should have a working knowledge and understanding of the mental health act, mental capacity act, disability discrimination act and disability rights issues.