The BBC reports:

Legal action has been dropped against a 15-year-old who faced prosecution for branding Scientology a "cult".

The teenager held up a sign which read, "Scientology is not a religion, it is a dangerous cult", in May outside its headquarters in the City of London.

City of London Police said it had received complaints and warned the teenager to get rid of the sign as it breached the Public Order Act.

More on the incident in this post. Here's my question:

A Crown Prosecution Service (CPS) spokesman said: "In consultation with the City of London Police, we were asked whether the sign was abusive or insulting.

"Our advice is that it is not abusive or insulting and there is no offensiveness (as opposed to criticism), neither in the idea expressed nor in the mode of expression."

Can anyone who is familiar with English law tell me what "abusive," "insulting," and "offensive," which are apparently terms of art, mean? ("Abusive" and "insulting" appears to be the statutory test; "offensive" seems to be the Crown Prosecution Service's interpretation of the terms.)

I would think that calling a religion a "cult" would be offensive and insulting in the lay sense of the word -- it may be quite right, and it should certainly be constitutionally protected, but despite its being offensive and insulting, not somehow "there is no offensiveness" there. So what's the legal rule in England about what's allowed and what's not?