I can't believe I've got so interested in this topic, I think it's a combination of it being a matter of principle, and my love of chasing down details...
The Current Doc T only came into force in 2024, but there were plenty of regs concerning toilet facilities prior to that - not just workplace regs, but documents like BS 6465, Doc G, Doc M, etc.
These regulations were based on the established pattern of men's, women's and accessible toilets; Doc T seems to have been prompted by the trend towards 'unisex' toilets replacing single-sex provision, and re-asserted the requirement for, in the first place, single-sex toilets.
The intention to do this was signalled in 2022, so there was plenty of warning that buildings would have to comply with Doc T.
You make a good point, PencilsInSpace, about Doc T not just applying to new buildings constructed since 2024, but it also applies to 'material alterations to existing toilet facilities in non-domestic buildings'.
So removing single-sex toilets in old buildings and replacing them with all mixed sex/'gender neutral' toilets is subject to, and does not comply with, Doc T.
It also makes no sense economically - the existing configuration [including an accessible toilet] plus the addition of a mixed sex toilet is perfectly adequate, so why the unnecessary expense and disruption, especially as the result may be in breach of building regs.?
Answers on a postcard please.....🙄
This is a commercial company's website, but I think it's a useful no-nonsense guide:
Navigating Approved Document T: Modern Washroom Design and Compliance Made Simple - Dunhams