Nigel: sorry to be pedantic, but: "Curiously, there's no such thing as a double affirmative signifying a negative. Yeah, yeah!". Go back and read my post again. (BTW, don't this as a criticism: I don't read everything either!)

I'd class "We don't need no education" as ironic use of ungrammatical colloquial speech; it's meant to reinforce the message of the song. Where did PF go to school? I think they had a better education than you might infer.

Steve