Well, the UK regime has the legal power to lock up an entire Celtic supporters' crowd indefinitely without access to a lawyer under present anti-terrorism laws for the sort of stuff they routinely sing, so I think they've taken care of the complaining for you.

What I could follow of that Rangers song (the YouTube sound was appalling) seemed like fairly innocuous banter to me.

I don't know why they bother having football teams at all, surely it's more fun for the opposite sides to just sing songs about Thompson guns and being knee-deep in blood at each other?