Unfortunately, it is also one of the crimes with the highest rates of false testimonies being cleared later onwards, at least on the continent.
Legally it's insanely complicated. Firstly there is the act, which is legal between consenting adults but criminal for either one of them, if the opposite after the act decides to deny said content.
On the other hand, as the act is legal, the CPS will have to prove not only the act but also prove, that no consent was given. Yes, if the defendant admits the act but claims consent, the CPS and victim will have to prove the lack of consent. A great many *struggle cuddle* accusations fall on that behalf, and from a legal point of view, they should too.
I am a bit disturbed about the hole "too intoxicated to consent" thing. In reality it's a reversed burden of proof, which in return is bang on breach of the millenia old western law principle of not guilty til proven otherwise, which just so happens to be a principal human right too.
The "drunk means no" rule is a great rule of thumb for all sorts of horny youngsters of all ages, but in reality it is a false safe. Any alledged victim with a modest hangover can claim this principle the day after and effectively force a sex partner into a criminal case - with reversed burden of proof !
As *struggle cuddle* is a hidious crime, it can appear fair. But would you think so did it apply to murder, tax fraud and kidnapping ?