> A constable may arrest without a warrant to prevent the person in question [from] committing an offence against public decency (subject to subsection (6))

I'm not sure of the specifics as to what "public decency" means in the UK but I believe your implication. I think subsection 6 supports my 'theory' (read: wild accusation)? Seeing as it was posted on the internet and could reasonably be avoided.

Even if that's not so, this seems like a tort and should not be handled by the police. Just my opinion.