Yet again 'case by case' gets rolled out by the TRAs as meaning 'we get to decide on the basis of each individual person'. Clearly that’s preposterous and unworkable. And it doesn’t mean that. It’s been discussed many times before on here.
Here are a couple of quotes from posts which made things helpfully clearer:
Case by case meant that each group that wanted to exclude one sex, had to be able to justify why that was necessary in their case. [my bold]
Stonewall spread the lie that case by case meant women’s groups had to justify excluding each and every man who claimed he was a woman individually on a case by case basis
Case by case was supposed to be the overall case not individuals. So the case would be for example- is this an area where staff change into work uniforms? Yes then it must be single sex. That's the regulations.
It was interpreted as referring to each person and has just been 'does this person want access? Yes so let's allow that'
ETA: the fact that they’re still banging on with the clearly incorrect interpretation appears either wilful or worryingly dim. Though IANAL.