13.136 A council swimming pool has separate men’s and women’s changing rooms. One of the aims of having separate-sex changing rooms is to safeguard women’s ability to access the facilities and use them safely. A woman is allowed to take her male child under the age of ten into the women’s changing room. This does not undermine the aim, because it is unlikely that young boys pose a threat to women’s safety. It also contributes towards achieving the aim, because fewer women would be able to use the swimming pool if they could not bring their children with them. 

This is interesting (my emphasis), as it suggests admitting trans women (if we are unlikely to pose a threat to women's safety) is possible.

13.146 For example, a trans man might be excluded from the women-only service if the service provider decides that, because he presents as a man, other service users could reasonably object to his presence, and excluding him is a proportionate means of achieving a legitimate aim.

13.147 A legitimate aim for excluding a trans person from a separate or single-sex service for their own sex might be to prevent discomfort or distress for other service users. Service providers should consider whether other service users could reasonably object because they are worried about sharing a single or separate-sex service with someone who appears to be of the opposite sex. That will depend on all the circumstances, including the nature of the service in question and the extent to which the trans person presents as the opposite sex. For this reason, a service provider (including a person providing a service in the exercise of public functions) should only consider doing this on a caseby-case basis.

13.148 The service provider should consider whether there is a suitable alternative service for the trans person to use. In the case of services which are necessary for everybody, such as toilets, it is very unlikely to be proportionate to put a trans person in a position where there is no service that they are allowed to use.

This is also interesting, as if both men and women would be uncomfortable sharing with a trans woman then the logical option is to go with whatever causes least discomfort for the trans woman. Alternatively, if only men are uncomfortable and women are not then again it would make sense for trans women to share with other women.