As the law stands at the moment, if you’re building a new non-domestic building or changing the function of an existing building and you have three toilets, each of which is a single room containing one individual toilet and a sink and which can be locked from the inside, then cannot all be accessible to everybody. One must be exclusively for women and one for men. And, as per the new guidence, which one someone can use is solely to be determined by what gender they were assigned at birth

Yes, it’s incredibly stupid, but that’s what the law currently says