Yes, Minister, Series One (1986)

[Bernard pulls the Prime Minister away from Luke for a private conversation.]

Hacker:
You just said that the Foreign Office was keeping something from me! How do you know if you don't know?

Bernard:
I don't know specifically what, Prime Minister, but I do know that the Foreign Office always keep everything from everybody. It's normal practice.

Hacker:
Who does know?

Bernard:
May I just clarify the question? You are asking who would know what it is that I don't know and you don't know but the Foreign Office know that they know that they are keeping from you so that you don't know but they do know and all we know there is something we don't know and we want to know but we don't know what because we don't know! Is that it?

Hacker:
May I clarify the question: Who knows Foreign Office secrets, apart from the Foreign Office?

Bernard:
Oh, that's easy: only the Kremlin.