Well British Gymnastics have made it clear that this is 100% about transgender people and nothing whatsoever to do with being intersex, so no, it's not. So probably best to put that discussion to the side.
The specific phrase is "identify with a gender that is different from the sex they were assigned at birth"
This is actually a phrase loaded with agenda.
"identify with a gender"
but this will get you access to 'single-sex' facilities. So in fact you are identifying as a sex.
Why then do they say 'gender'? Because 'gender' implies something that is a mere personality trait, a preference, and therefore changeable.
"that is different from the sex"
OK so they are saying here that gender and sex are different. Someone can 'live in a female gender role', whatever that means, despite having a penis and therefore biologically being a man..
"they were assigned at birth"
But now they are implying that there might be some error, or that biological sex is changeable.
In terms of the subject of this policy (transgender people) the correct term is
"your biological sex" - which cannot be changed, and is indeed not 'assigned', but rather a matter of objective fact
To the extent that there is a gender/sex distinction, it would be 'gender' which can be 'assigned', in the sense that girls may be brought up from birth in pink etc. and boys in blue.
So a slightly better phrase is "identify with a gender that is different from the gender they were assigned at birth".
However I am not clear that that phrase is yet accurate. 'Assignment' implies something slightly more active. 'I was assigned to Iraq'. Some people deliberately do NOT 'assign' a gender to their newborn (say) boy baby, yet that doesn't make the boy transgender.
So the actual question is
"identify with a gender that is different from your biological sex"
The question is why do we need
"the sex they were assigned at birth"
when "biological sex"
says the same thing, and the answer is we do not - it's part of an agenda to erase biological sex, to indeed erase biology itself, and say everything is merely a matter of preference, and probably those silly doctors were mistaken when they saw your penis, which is actually a lady dick don't you know.
And if you ask where it comes from, well you can look at the 2004 Gender Recognition Act.
www.legislation.gov.uk/ukpga/2004/7/section/9
"Where a full gender recognition certificate is issued to a person, the person’s gender becomes for all purposes the acquired gender (so that, if the acquired gender is the male gender, the person’s sex becomes that of a man and, if it is the female gender, the person’s sex becomes that of a woman)."
This appears to reflect concerns from decades gone by, where we were worried about things like 'sex discrimination' (i.e. women being less favourably treated).
See this Parliament Committe from 2003 during the drafting:
publications.parliament.uk/pa/jt200304/jtselect/jtrights/34/3416.htm
In other words you had all this legislation that was drafted saying that there were distinctions based on people's sex, and the 'Gender Recognition Act' ripped it all up in one fell swoop. Biological sex was abolished and replaced with gender, yet this was not done explicitly, and this disingenuousness continues today.