I take your points, MyAmpleSheep, and I know that the mishmash or rules has happened over a long period of time in different contexts e.g. building regs, health and safety etc..
And therefore I disagree with the suggestions that the confusion is solely the fault of TRAs - they have exploited apparent contradictions shamelessly, but not without some foundation in fact.
I would make the point though that 'forcing every employer and commercial landlord to refit to meet Document T' shouldn't be that much of a problem.
Doc T's requirements don't look very different from what has been the standard configuration for yonks: most public buildings already have separate men's and women's toilets, and have added accessible ones.
So the only employer and commercial landlords who would have to make drastic changes would be ones who decided at some point to make the expensive, disruptive and arbitrary decision to do away with single sex toilets, and make them all 'gender neutral'.
Any venue that chose to add gender neutral toilets to its existing single sex ones would have no problems meeting the requirements of Doc T.
I admit I may be over-simplifying a bit, but I don't care -it's an antidote to 'it's all so terribly confusing, it's easiest to make all toilets mixed sex'
I think I may change my username to Keeptoiletssimple