The force said a man was arrested on 1 November on suspicion of using a public communication network to send offensive messages and other offences.
I think there may be more to this story than just "wearing an offensive costume", but without seeing what was said in the posts that's sheer conjecture.
Edit
Turns out there was more to the story! Whodathunkit!
Maybe you should look up the definition of hate speech.
I'm not saying it's what happened here, but the idea it's about "offense" is something worthy of the Daily Mail. The law doesn't deal with opinion in reality, only headlines.
Yes... That's exactly what I've been saying, your right to free speech ends when it becomes hate speech. I'm not really sure what point you're trying to make.
Re: your edit. Are you trying to say that hate speech should be allowed? I'm genuinely baffled.