The question is whether the victim in question was in a possition of being able to consent. This is left to the jury.
For guidance, in the leading case a woman went out with two men, vommed all over her own hair, which one of the men cleaned, then 'gained conciousness' whilst having sex, but didn't resist at this point. The man was declared not guilty of rape, despite her claiming she was too drunk to be able to consent. Therefore, guidance seems to be that being very drunk is not good enough to land a rape claim.
Furthermore, just because somebody doesn't say "no" or resist, doesn't stop it from being rape either.
I can confirm with confidence that this is how the law stands today. Obviously each case is decided on it's individual facts, which may seem neglible to the non-lawyer.