Of course I can't say what happens elsewhere, but in general, there's a lot of myth and misnomer about this sort of thing: This is an increasing area of work and it an area very poorly understood by ambulance personnel; and historically has been very poorly taught.
As a contrasting example, our framework is:
1) Prevent suicide if it is imminent or an attempt is in progress - this is very rare,
2) Assess pt for injuries or poisoning requiring immediate treatment and/or referral,
3) Differentiate between a) attempted suicide, b) a genuine and significant threat to commit suicide, or c) self-harm
4) If (a) or (b) above are present then arrange a psychiatric assessment for the patient.
The key factor in determining if either a "suicide attempt" or "genuine and significant threat to commit suicide" is present is by answering the question "did the patient intend to die?". The answer is most often "no" but sometimes it is "yes"; for example, somebody who drank (or attempted to drink) a bottle of dishwashing liquid or some other less-than-lethal substance but clearly articulated (either to ambulance personnel or somebody else present or who they were in contact with) that this was with the intention of dying has made not only a significant and genuine threat, but has also seriously attempted suicide. In contrast, somebody who, in the "crux of the moment" just said "oh bugger you, maybe I should go off myself" and then nothing further is said did not.
Patients who have made a genuine and significant threat to commit suicide, or whom have attempted to commit suicide, require a psychiatric assessment. Locally, this is done by our area community mental health people. They can see patients in the community so transport to ED is not routinely required unless there is absolutely no other reasonable option available; i.e. nobody can stay with the patient until they arrive (they often take one to three hours, or will visit in the morning). These assessments are much more detailed than what ambulance personnel can perform.
Patients with only self harm are not routinely referred for an assessment and are referred to their GP.
The Police are not routinely required because they don't have any special powers to assist. They cannot arrest people who've not broken the law. If police restrain somebody to assist ambulance personnel, technically that person has been arrested and as they have not committed a crime, that is illegal and the person can (and several have) successfully prosecuted the police for false arrest. They are only involved if there is significant danger to other persons.
This might be wildly different to how you do your thing, and it would be a shame if that is the case. I've dealt with enough of these patients to know routinely transporting them, or routinely involving the police, is not the best thing; it's the last bloody thing they want. It often just ends up making the situation worse.
