I realise that there's more to it than just Document T of Building Regs - it is only applicable in England, I believe, and it would be useful if somebody chased up the equivalent regs for Scotland, Wales and NI.
Many of the examples MNers are complaining about have in fact been in England, e.g. the OP is about Somerset.
The Building Regs mostly cover new buildings, but they refer to 'building work'. I've chased up the legal meaning of 'building work':
The legal term ‘building work’ generally includes building new buildings, making buildings bigger, altering buildings and changing what they are used for. It also covers installing a ‘controlled service’ or a ‘controlled fitting’
Manualtobuildingregs-July2020.pdf
IANAEOUKBR - I am not an expert on UK building regs
but it seems to me that replacing existing toilets with some form of unisex provision is 'altering buildings' and 'installing a controlled service or controlled fitting'
The regs were updated in 2024, so they are the most recent regs about toilet provision.
They couldn't be clearer about the primacy of single sex toilets; note the use of 'must' and 'may', and 'in addition to'.
Building regs T1.
(1) Toilet accommodation in buildings other than dwellings—
(a) must consist of—
(i) (ii) reasonable provision for male and female single-sex toilets, or where space precludes provision of single-sex toilets, universal toilets, and
(b) may consist of universal toilets in addition to single-sex toilets.
(2) In this requirement— “single-sex toilet” means toilet facilities which—
(a) are intended for the exclusive use of persons of the same sex, and
(b) provide washbasins and hand-drying facilities in—
(i) either the toilet room or cubicle, or
a separate area intended for use only by persons of that sex.
...
“universal toilet” means toilet facilities which—
(a) are provided in a fully enclosed room which contains a water closet and washbasin and hand-drying facilities, and
(b) is intended for individual use by persons of either sex.
Toilet accommodation: Approved Document T
Removal of required single sex toilets and their replacement with unisex provision which may or may not comply with the official definition of a 'universal toilet' seems to be happening a lot. It looks like it is not compliant with current regs, but that's just my opinion - see 'IANAEOUKBR' above!
What is the motivation for this, when segregated toilets work OK for the vast majority of the population? Why all this unnecessary expense and disruption?
The word I've used for a lot of the TRA response to the SC ruling is: spite.
Women may have won the right to exclusive use of women's spaces, but we can still deny them their rights by physically getting rid of single-sex spaces.
This looks like a spiteful scorched earth campaign against women's spaces