No it isn’t.
The law is very clearly stated in the equality act, and the clarification from FWS at the Supreme Court.
Services are not allowed to discriminate against any protected characteristic except where discrimination (in a neutral sense of the word) is a proportionate means to achieve a legitimate aim.
One example of a “legitimate aim” is the use of single sex facilities to protect the privacy, safety and dignity of females from the presence of males when they are dealing with private bodily functions.
Providing single sex spaces is the proportionate means - female people are half of the population and it is reasonable to assume that the majority of them do not want to come across a male person in such a space.
”Case by case” is situation specific eg. Provision of toilets in shopping centre for example. If the owners of the centre want to provide separate sex spaces alongside other options, the equality act allows this act of discrimination because it is a proportionate means to achieve a legitimate aim.
Once the single sex space is established, there is no “case by case” assessment of each male person who wants to come in.
You seem to be suggesting that we need case law to establish that males do not have the right to access services for females on an individual basis.
This is bollocks.
You are basically saying male people should carry on using the female spaces and services because individual women can’t physically prevent this in moment but will have to complain to the service provider for not enforcing the rules, and then take them to court. This sounds a bit like using male power to make women put up with situations they don’t want. All a bit VAWG.
I don’t know what “case law” you are hoping for? The service provider can refuse service to anyone who is repeatedly making a nuisance of themselves.