In the example I gave earlier, the female has obtained consent from her partner. The male changes his mind half-way through but does not stop or act in any different way.
In cases such as these, my understanding(and gut feeling really) is that since knowledge of consent is what makes an action legal, the person had no knowledge consent was revoked, and cannot be charged for something that is impossible to avoid being guilty of?
If the other party is not signalled that consent was withdrawn, then it is, in my mind, a bit tricky. It means that consent was no longer there, but the other party didn't have any way of knowing. I think it's fair to say that no assault occurred, but it's still damaging to the one no longer wanting to have sex. In that case it's really unfortunate for both parties :-(
It's like signing up for a phone contract, then deciding you don't want it any more and stopping using the phone. If you don't tell the provider then they're completely within their rights to keep billing you.
It depends on the way the law is written. You can certainly be guilty of criminal offenses absent any understanding or intent.