Sorry for your troubles,
@mossy71, hope things are being resolved now. I must stress I know nothing at all about type 1 diabetes, nor insulin/glucose regimes, so cannot comment on any aspectof that.
Just a couple of points strike me - and fully my own point of view: a) is there anyone who can verify what, and how much, your son drank that day/night? b) you say that having called the police, when you went back to the lounge your son got up to give you a hug (are you sure that was his intent?) (presumably he wasn't very steady on his feet at the time?), and that somehow things then went pear-shaped. Neither you nor your husband saw your son head-butt the police officer. Both of you separately need to think carefully through your recollections of the sequence of events. From the comments in your post no.5 it appears that the police might have over-reacted using the pepper spray in your lounge. Did they assume that in moving towards you, he was about to do you some harm? When was the head-butting supposed to have taken place? Even if it did (& it's by no means clear that there was a head-butt at all), was it an accidental thing, that happened because of his unsteadiness, fear, flopping about, the police grabbing him? If no bruise or mark of any sort, then if it happened, it must have been fairly mild/ineffectual. That's not the same as a definite, determined effort to head-butt whilst in control of one's faculties. Did the police officer seek medical assistance? Don't accept the "technical difficulties with the body cam". If the police can't produce the evidence, then you must insist that it is argued against by the solicitor very strongly. - it is a record that potentially could stay with your son for a very long time, and have consequences on his life, even after it is "spent". Guess I'm saying don't let yourselves be railroaded, just because you 'know' your son was drunk, and you're feeling a bit guilty on his behalf - there might have been more than the alcohol going on at the time - every aspect needs to be taken into account. Plus it was a Saturday night, and the police may have arrived at your house already fed up with yet another Saturday-night drunk (sorry).
Apols if this sounds unsympathetic to police, but reading what happened (and recognising that we have only one person's perception) there does appear to have been a lack of knowledge, understanding, or whatever on this occasion. We don't know whether they did, in fact, give glucose / insulin as needed - did they call medical help for him when at the station, or simply a quick exam and then leave him all night to sleep it off, assuming it was just the alcohol. You'll need to see evidence of all actions, and challenge anything that doesn't sound/read right. Not saying police should be perfect - but they should know enough to know when they don't know enough, and should know where to go for guidance - Saturday night notwithstanding. Providing all's hunky-dory with the police, then your son will have to live with the consequences. Glad to see that he's feeling the contrition now - let's hope it continues at least till the New Year's passed.