Unless he has negotiated a “basis of plea”, when a defendant pleads guilty he accepts the prosecution’s version of events in full taken at its highest. No witnesses are called, no evidence is produced. There is no need. Evidence is only produced and witnesses called if the defendant pleads not guilty (when a trial to establish his guilt or innocence will be held) or if he disputes crucial elements of the prosecution’s case (when a “Newton Hearing” will be heard to establish the facts). Neither of these hearings will be heard immediately a plea is entered. This is to give both sides the chance to prepare their cases.
If the allegations of threats were made by the security guard and put into his statement, those allegations will form part of the prosecution’s case, and part of the information put before the magistrates when they make their decision on sentencing.
I cannot see any justification for the magistrates sending your son to court unless such aggravating features were present. See page 33 of the magistrates sentencing guidelines here:
http://www.sentencing...pdate_1__2__3_web.pdf
I don’t think there is much more I can usefully add.