I honestly find difficult to unravel what you are saying, much like Helen Webberley's pronouncements.
In the Example Helen Webberley gave of a child observing two distinct groups (males & females) in the playground & categorising themselves according to who they thought they had more in common with pretty much sums up gender identification.
That's one possible interpretation of the behaviour of a young child who, in Webberley's example, decides to join the line of boys if they are a girl and vice versa. Its weakness as an explanation is that it relies on the hypothetical existence of "gender identity".
people don't usually 'verify' their categorisations via gonad or chromosomal tests how would you know those 'readings' are generally reliable ? Self evidently, biological variation exists outside of normal ranges not to mention technology has provided for confounding alterations. As far as there being only a minority of cases that are outside the normal ranges its impossible to know the true extent given we haven't tested for billions of people.
There are estimates for the number of people born with DSDs/VSDs. Most of these very rare conditions would not result in any ambiguity at all about the sex of a person in a "social context" or any other context, including when a child is born. Start on this page:
www.dsdfamilies.org/parents/what-dsd/brief-overview/conditions
Only two DSDs are relevant to potential ambiguity about sex in a social setting: 46,XY DSD with female phenotype and 46,XX DSD with male phenotype.
(I have not included 5ARD as it is phenomenally rare, children go through male puberty and would then be perceived as male plus in the unlikely event that a child was born with 5ARD in the UK they would be subject to genetic testing so would be raised as male from birth.)
- 46,XY DSD with female phenotype (e.g., CAIS): Prevalence of 6.4 per 100,000 female births (~3.2 per 100,000 total births), representing ~25% of 46,XY DSD cases. These individuals are typically raised and identified as female socially, despite XY chromosomes.
- 46,XX DSD with male phenotype (e.g., XX testicular DSD): Prevalence of 1 in 20,000 males (~2.5 per 100,000 total births), representing ~20-30% of 46,XX DSD cases. These are usually raised and identified as male, despite XX chromosomes.
References:
- Berglund et al. (2016). Incidence and prevalence of 46,XY females. J Clin Endocrinol Metab. Link
- MedlinePlus. 46,XX testicular DSD. Link
- Österman et al. (2024). Prevalence of DSD in Switzerland. medRxiv. Link
Those figures translate to an estimated total of less than 3,000 people in the UK from babies to adults age 85+
The number of adults who identify as transgender in the UK might have been possible to estimate if the questions in the most recent census had not been so confusing. All we know is that the census provides an over-estimate given that the highest returns are for boroughs with a high percentage of people who do not have English as their first language.
"The Census 2021 estimate is that 0.54% of people in England and Wales aged 16 years or over had a gender identity different from their sex registered at birth. The majority (93.46%) of people responded that they had a gender identity the same as their sex registered at birth and 6.00% of people did not answer the question. The 2022 Census in Scotland found that 0.44% of people aged 16 years or over were trans or had a trans history."
https://www.ons.gov.uk/peoplepopulationandcommunity/culturalidentity/genderidentity/articles/census2021genderidentityestimatesforenglandandwalesadditionalguidanceonuncertaintyandappropriateuse/2025-03-26
This gives an estimate of 289,400 people who identify as transgender aged 16 or over. The vast majority of whom will not "pass" unambiguously as the opposite sex.
Estimates based on self-reporting are that 24% are "never clocked" as either transgender or as their actual sex.
https://transequality.org/sites/default/files/docs/usts/USTS-Full-Report-Dec17.pdf
However, IMHO this is very likely to be an over-estimate, given that the majority of people on social media who identify as transgender and who claim to "always pass" do not in fact remotely pass online when they are not using "filters" and/or where their height is apparent and/or they speak.
Being generous, let's say 10% of females and 5% of males, giving a total of 43,400 people aged 16 or over in the UK who unambiguously "pass" as the opposite sex in social situations.
TBH this still seems a rather high number, from personal experience of meeting people in real life who I was later surprised to learn identified as transgender.
This made sense of what at the time had seemed something strange about the people concerned. When I learned that they had been medicalised to mimic the opposite sex it made sense, as I realised that what had seemed strange was a mismatch between their behaviour and what I had erroneously understood to be their sex.
Holly Lawford-Smith has suggested that it is hypothetically possible for a female to successfully "become" a man but that it is not possible for a male to successfully "become" a woman, ie. to be capable of identifying as the opposite sex. That is not to say that any such female would necessarily "pass" as a man in a social setting.
Trans Men Are Men (But Transwomen Are Not Women)
https://hollylawford-smith.org/trans-men-are-men-but-transwomen-are-not-women/
Similarly, someone might "pass" as the opposite sex but not actually identify as the opposite sex. Such as people who are androgynous, which is to do with perception of appearance, presentation and possibly behaviour, independent of any claimed "gender identity". Still likely to be very few and far between.