Well, looking at this link, it seems like this is significant.
https://labour.org.uk/resources/supreme-court-judgment-faqs/
Can we operate an All Women Shortlist (AWS) for our upcoming selection process?
The Party can use single sex shortlists lawfully only when biological women are underrepresented among the Party’s current cohort in the relevant legislative body. For example, the AWS provisions in the Rule Book may only be applied in local government selections where the Labour group is not currently comprised of a majority of biological women.
Can we include trans women in an AWS?
The Supreme Court judgement has clarified that all-women shortlists must be single sex. This means that only biological women are eligible to apply for selections run on the basis of the AWS provisions in in the Rule Book.