That case was won by the male in question only because at the time the statutory guidance given by the EHRC, which is legally binding, misrepresented the law.
EHRC very quietly changed its guidance last year by deleting the erroneous passages. Another case like this, the landlord would win. And rightly so.
Also I've seen plenty of masculine women, feminine men and males and females who identify as trans. I've never mistaken a woman for a man, no matter how butch.
The only ones that come close to passing at first glance, from a distance or in photos are women who've been on testosterone for a long time (although their size and shape tend to give them away) and men who've had serious amounts of feminisation surgeries (although for me their size, movements, behaviour, voice modulation and mannerisms tend to give them away).
Generally speaking only males who finish transitioning medically by their early 20s have a chance of truly passing as the opposite sex in the eyes of women. IIRC, that's 1 in 10 transsexuals and 1 in 100 of all men claiming womanhood. So you're far more likely to encounter an obvious male than one who passes.
And those operating toilets can and some do, of course, enforce sex segregation. But what is far more important is the social taboo that has kept men out of women's toilets. There has never been an equally strong taboo in the other direction because women generally avoid the men's and they are putting themselves at risk, but that isn't true the other way around.
As for if women use the gents why can't men use the ladies?
I have never used the gents, I doubt I ever will. And just because some women have done so in an emergency doesn't mean all of us lose the right to female only facilities. It means that toilet providers must try harder to ensure there are enough women's toilets.