It does indeed mean that. It doesn't, however, mean that the instructions have to be accompanied by your signature.
No it's not (necessarily so). What you describe may be the result of a mistake and, if it were, it would not be illegal and no amount of posturing will make it so.
I know this is widely cross-posted but one of the groups is uk.legal. It's not uncommon there for someone to ask a legal question, be given the correct answer and then try and argue that the law is what they think it should be. If you want to argue that the law should be changed, that's fine, but there's no point in trying to argue in uk.legal that something is illegal when it's not.
Mike.