"Visibly shocked" bystanders and why haven't they come forward? 'Visibly shocked" are words which often appear in police reports. It's police language for something like 'people in the hearing or sight who of the man and who were likely to be caused alarm,harassment or distress, were so' ! To justify the arrest, if any, the fact that the man used rude words to the policeman himself would not be sufficient. He has to be causing a breach of the peace; in this case he would have been arrested under section 5, Public Order Act, which requires some proof of others being alarmed etc, or likely to be, by his words or conduct.
It's unrealistic to expect either that the police will take particulars of passers-by or bystanders, even if they have the manpower to hand, just so witnesses can say in court 'I was/ was likely to be alarmed.." or that this disturbance is one which will have bystanders rushing to the nearest officer or police station to report what they've seen. It's not a stabbing or riot!