In America, however, TERFism today is a scattered community in its death throes, mourning the loss of its last spaces, like the Michigan Womyn’s Music Festival, which ended in 2015. And so the strangely virulent form that TERFism takes in Britain today, and its influence within the British establishment, requires its own separate, and multipronged, explanation.

Ms. Parker and Ms. Long may not know it, but they’re likely influenced by the legacy of the British “Skepticism” movement of the 1990s and early 2000s, which mobilized against the perceived spread of postmodernism in English universities as well as homeopathy and so-called “junk science.” Hence, the impulse among TERFs to proclaim their “no-nonsense” character; witness the billboard Ms. Parker paid to have put up last fall dryly defining a woman as an “adult human female.” Such a posture positions queer theory and activism as individualistic, narcissistic and thus somehow fundamentally un-British.

It’s also worth noting that the obsession with supposed “biological realities” of people like Ms. Parker is part of a long tradition of British feminism interacting with colonialism and empire. Imperial Britain imposed policies to enforce heterosexuality and the gender binary, while simultaneously constructing the racial “other” as not only fundamentally different, but freighted with sexual menace; from there, it’s not a big leap to see sexual menace in any sort of “other,” and “biological realities” as essential and immutable. (Significantly, many Irish feminists have rejected Britain’s TERFism, citing their experience of colonialism explicitly as part of the reason.)

But perhaps the biggest factor in the rise of TERFism has been the relative dearth of social movements in Britain over the past three decades. It’s telling that Ms. Parker thinks it was the United States that exported “political correctness” and ideas like “gender identity” to Britain; it might even be fair to say that she’s right.

In other parts of the world, including America, mass movements in the 1990s, 2000s, and 2010s around the effects of globalization and police brutality have produced long overdue dialogue on race, gender and class, and how they all interact. In Britain, however, the space for this sort of dialogue has been much more limited. As a result, middle- and upper-class white feminists have not received the pummeling from black and indigenous feminists that their American counterparts have, and thus, their perspectives retain a credibility and a level of influence in Britain that the Michigan Womyn’s Festival could have only dreamed of.

Curiously, Ms. Parker and Ms. Long’s trans-Atlantic jaunt has led to a split in the ranks. Over the past few days, large segments of British TERFism have disowned both of them on social media for their Washington stunt, calling it an “ambush,” and them a “liability.” Whether Ms. Parker and Ms. Long went too far for a movement that, to date, seemingly has yet to hit a low, remains to be seen.

It is revealing, however, where Ms. Parker feels she still has friends: On her same trip to Washington, the woman claiming to be a feminist, standing up for the rights of lesbians everywhere, made sure to drop by the right-wing Heritage Foundation.

Sophie Lewis, a feminist theorist and geographer, is the author of the forthcoming “Full Surrogacy Now .”