Buildersmate has come up with his usual sound sensible advice, I would like to add a couple of extra things. As far as I know if your son has worked for the company for over a year, then he cannot be sacked 'on the spot'. If it is serious, i.e theft or other serious misconduct, then the person would be suspended to allow the company to do an investigation.
The company should have given your son a letter stating the reasons why he has been suspended and they must by law give 24 hours written notice for him to attend a hearing.
Your son should be allowed to take someone else in with him at the hearing, normally a union member or another fellow worker. He should be allowed as Buildersmate has said, to give his version of events and to state any mitigating circumstances in his favour. The company should at some point, have a break in the meeting to make their decision. They may give their decision after this break, or may take some days to decide on the course of action taken. They should then provide a way of appeal if your son feels that the decision taken is unfair.
As Buildersmate has stated, if it is serious, it is possible that your son could be dismissed for gross misconduct, or they could decide on a warning. If they decide on a warning, it does not have to start at a verbal, they can decide to jump straight to a final written if the offence warrants this.
I feel that the action taken does look serious for your son and would suggest that you take further advice to ensure that the company has followed correct procedure, if they have not, they could be handing your son a route to win a tribunal appeal for unfair dismissal, even if they have good grounds to sack him.
All the best, Sue