Hi Deb:
Firstly, I can understand your concern and, though it's easy for me to say, try not to get yourself too worked up.
Your son has been charged with what can be described as the least serious of the public order offences under the POA 1986.
He cannot be sent to jail, if convicted, these 2 sections would bring fines at most.
Section 5 basically refers to disorderly behaviour in a public place, i.e. shouting, swearing etc.
Section 6 is added on if alcohol has played a part and, given that you've said he was held in the cells for 21 hours, I'd have an educated guess that he WAS well drunk. I speak from experience (NOT of being drunk).
Was he interviewed when he sobered up? If so, he should have had a solicitor present. In which case, contact the solicitor regarding fees etc (The Police Station solicitor would have been free, if he was interviewed.)
If not interviewed, I'd advise him to contact his local Citizens Advice Bureau or the Law Society re fees.
If convicted, it would mean that, yes, he would have a "record" albeit for a very minor offence. It would be best for him in the long run to declare it to his firm IF he is required to do so.
If he pleads guilty at Court (It's undoubtedly Magistrates Court he has to attend, yes?), then it should be dealt with there. I believe it would also be Mag Court if he pleads not guilty too.
Hope this is of help. Feel free to ask again if you wish.
Good luck.