I think the guidance (if not the law) to the police is that they have to tell the potential offender not to use those words, or "don't swear at me" first, and i

I think the guidance (if not the law) to the police is that they have to tell the potential offender not to use those words, or "don't swear at me" first, and if they still continue then they can be nicked. So they have to know that what they are doing is abusive first. In other words you can swear at the police but only once!