Annandale, I'm coming to this somewhat late, and have had to piece together what happened, but I'd like to offer a shred of comfort that, given my experience of mental health services over the last 6 months, nothing you did yesterday would have reliably changed anything.
My mother was sectioned for 3 months, 6 months ago. In the 3 months she's been out of hospital, every time she's seen her psychiatrist, she's been prescribed a drug at the wrong (unobtainable) dose, then nobody, including crisis team, A&E, 111, etc., has been able to do a thing about it, until a day or two later, when it's corrected by the original doctor (when her CPN tells him off).
If you had gone to A&E, you may have had an assessment, or you may not, and it may have been useful or not. You followed advice and did your best.
It isn't your job to risk assess. Don't let that weigh on your shoulders.