This is a law that has been brought in mainly to address date rapes and where a woman in incapacitated with drink, etc. Clearly someone who is incapacitated cant say yes or no.
This is a good thing.
Where I worry is as follows.
First, it is impossible to prove someone said 'yes'. If a woman says 'yes' and then make a complaint it is still one person's word against another.
Second, does a man literally have to ask a woman formally 'do you want to have sex' in order to have a defence? In many cases, sex does not really happen like that but is a mutual act where a series of acts lead up to sex. That is why in the past a jury often threw out cases because a woman acted like 'she was agreeing', for example by agreeing to accompany him to his flat or 'inviting him in for a coffee' or 'flirting and dancing and drinking with him all night. In fact juries going back in history were looking for evidence of a tacit unspoken 'yes' evidenced by her actions. Look at what she did not what she said she said.
I can see defence barristers will still persuade juries that a 'yes' was unspoken but 'an implied yes' was given evidenced by certain behaviours a woman might exhibit and I can see juries being persuaded. Adults who have had sex know that women does not literally say 'yes lets have sex' every time she has sex. Its unrealistic and goes against human nature and behaviour. Do married couples literally have a stilted legal defence 'yes-no' conversation every time they have sex? Of course they don't.