Note that if you record everything with intent to disclose you are legally obliged to tell your interlocutor.

Well, yes. But playing it back to the person you spoke to is legal. As is submitting it to a court in evidence. You couldn't play it to the person's boss, though.

That would almost be better -- it would be kind of insulting to say it at the start of every phone call, but it might get people to get it right the FIRST time :)

Although quite often when you speak to a call centre, you are told that "calls may be recorded" - in absence of further specification about who may record the call, I've always thought that could be taken as an open invitation by either party.