Okay - this is the missing piece of the post-consent jigsaw for me.
For rape to occur, the man must have rape in mind. He must actually believe the woman has withdrawn her consent to sexual activity and then continue to have sex with her regardless of her wishes.
Otherwise, as state of mind is intrinsic to crime, a crime has not occurred. At least in law. I think. Actus reus is not enough. Mens rea is necessary for a crime.
So there is a burden upon a woman to make the withdrawal of her consent clear. Silence won't do once consent is provided.
It's a bit more complicated than I thought. But practically-speaking, much the same in almost all circumstances. But there's a little area of difficulty in there.