From the podcast I’ve been listening to, it’s not coming across that alcohol has featured a huge amount. Complainant 5 perhaps the most, but I didn’t get the impression that the defence made much headway with any suggestion that her memory was affected.
Generally, alcohol consumption can play a huge part in undermining a rape complainant’s evidence, as any doubt that something may have been said or done leading to a reasonable belief in consent can lead to acquittal, so if memories can’t be trusted, well you can see why the defence are going to want to explore that. I’m not really seeing that here though.
As an aside, a person can be deemed incapable of consent if they are incapacitated, and obvious drunkenness can invalidate the reasonableness of a claimed belief in consent, but then that can get complicated where the defendant was also drunk.
It’s all fact specific and case specific, but there are no restrictions on what the defence can explore if it’s relevant to the witness’s memory of events and those events are in dispute.