In November, the British high-street bank Metro announced that it was expanding its gender and title options. Customers could now register as “non-binary” rather than male or female, and as “Mx” rather than Miss, Ms, Mrs or Mr. In some ways, this development parallels the rise of Ms in the 1970s, which was popularised by feminists who wanted a title that didn’t identify women by their marital status. In practice, Ms marks women by their political affiliation instead (if you’re talking to a Ms, you’re probably talking to a feminist) but, even so, its first intention was to conceal rather than reveal information.

Mx does something different. To declare yourself a Mx is to disclose something about yourself: that your identity is outside what has become known as “the gender binary”, and you are neither man nor woman but something either in between or entirely other. This is a statement about who you are, and it comes with an implicit understanding that not being able to make that statement – or not having it recognised – is damaging. As the father of one gender-non-binary teenager told BuzzFeed UK: “When . . . you don’t identify as male or female and you only see those two boxes, then you don’t see yourself there . . . You are absent. That must hurt, and that’s what makes me angry.”

While users of Ms hoped that their title would supersede the ranking of spinsters and matrons, Mx relies for its meaning on the persistence of alternatives. You can only be non-binary if there’s a binary against which to define yourself. It is now recommended practice at some US universities for students to declare their preferred pronouns, and mandatory that these should be observed by others. Failure to do so is considered more than a breach of etiquette: “misgendering” is looked on as an act of bigotry, even a kind of verbal violence. This use of gender as self-assertion has an obvious appeal to teenagers and young adults as a parent-baffling subculture, but it starts much younger, too, with a small but growing number of primary-age children announcing that they are trans.

On one of its covers in 2014, Time magazine famously described transgender activism as “America’s next civil rights frontier”, but the proliferation of gender identity is at least as much a consumer choice issue. This was also the year that Facebook introduced its “custom” gender options, though it would perhaps be more accurate to describe them as “expansive presets”. Users can choose anything from “agender” to “two-spirit” via “bigender”, “gender questioning” and “transmasculine”, but what they can’t do is subvert the system by selecting an unapproved option. A feminist wishing to register her objections to the class structure of gender by typing in the word “oppressive”, for example, would be stymied here. However diversified gender identity becomes, it is a precept that everyone has one (if your identity and your body “agree”, you are said to be cisgender).

For some, asserting their identity is enough. For others, aligning their presentation with their sense of self will involve altering their appearance. At the least invasive level, that might demand cross-dressing. A natal female might choose to “bind” her breasts, flattening them to achieve a more masculine silhouette. Many seek prescriptions for opposite-sex hormones. At the most extreme, a trans individual will opt for surgical removal of their secondary sexual characteristics and gonads (more rarely, for surgical construction of opposite-sex genitalia), coupled with a lifetime of hormone replacement therapy.

Hormonal and surgical treatments have been possible only since the mid-to-late 20th century, and for many who choose them, these alterations prove life-changing in a positive way. But beyond the confines of the National Health Service, a consumerist edge to treatment becomes more obvious. There are doctors specialising in private transition medicine whose websites include statements such as “the only person that can actually diagnose [gender dysphoria] is the person living with the feelings”. In other words, the prescription is based not on a doctor’s medical judgement of the patient’s needs but on what the patient asks for (and is willing to pay for).

Plastic surgeons promise to transform transgender patients from “caterpillars” into “beautiful butterflies”, holding out the prospect of becoming one’s “true self”, in the same way they have long sold boob jobs and liposuction to women.

Not everyone accepts this brave new world. For conservatives in the United States, trans issues have become the next battle in the culture wars, and Republican politicians have introduced “bathroom laws” that would legally compel trans men and women to use toilets or changing rooms in line with their birth sex. Gender identity was an issue in last year’s US presidential election; a Tea Party-supporting talk-radio host tweeted: “If you want a country with 63 different genders, vote Hillary. If you want a country where men are men and women are women, vote Trump.” This vehement rejection of gender self-identification creates its own kind of identity politics.

That Donald Trump said that Caitlyn Jenner (the former Olympic decathlete whose transition became public in 2015) would be free to use “any bathroom she wanted” at Trump Towers did little to stop the perception that a vote for Trump was a vote against gender nonconformity. And, in some ways, Trump’s acceptance of Jenner’s right to use the ladies’ lavatories is not wholly at odds with the idea of a world where “men are men and women are women”: it’s just that some of the feminine people were born male and some of the masculine ones were born female. It is unclear what Trump’s presidency will mean for trans rights, but whatever happens in America will influence gender ideology worldwide.

Threats to legal abortion and equal marriage could strain some of the alliances within the trans, LGBT and feminist movements. A trans woman who has undergone surgery is in a very different situation from a male who identifies as a woman but does not want any treatment. A gay, lesbian or bisexual person who is discriminated against for their sexuality does not experience the same oppressions as a trans person (it is an article of faith that gender identity and sexuality are separate things, although in practice the division is not that neat). The political priorities of women who are victimised because they are female will not overlap perfectly with the priorities of transgender women – some of whom complained that the “pussy hats” and signs referring to female genitalia on the anti-Trump women’s marches in January were “exclusionary”.

Gender identity is now embedded in many people’s self-perception, as well as in day-to-day bureaucracy. But the messy relationship between sex and self is not going to be settled imminently.

Sarah Ditum is a frequent contributor to the New Statesman