I present the "why" and "where"...
"Mullen sang the song to officers on 25 July while sitting in the back of a police van after being involved in a fight in Blairgowrie, Perthshire."
I have a really really hard time believing the police arrested a man for getting involved in a fight, but the man did time in jail for something a lot more trivial. I mean, why wasn't a sentence passed down for the fight he got arrested for? If the cops and judges really were corrupt and conspiring to put this man away for singing "Spiderpig," you'd think they'd have the wits to sentence him to those 3 months in jail for the fight, if only to cover their own asses. But no, this seedy conglomeration of easily annoyed policemen and marionette justices were stupid enough to abuse their power and not try to hide it at all.
On the other hand, maybe (just maybe) the instance of "breaching the peace" was when the man got involved in a fight that the police had to break up, and the person who wrote the article manipulated the facts for the sake of having a more sensational story.