Don't look at the man behind the curtain ...
"It makes you wonder how the facial recognition works at international arrivals for certain UK airports since there's no Face ID-like depth analysis data on file with which to compare your real-life mug."
I hate to burst your Christmas bubble, but if you thought there as anything clever about the system, you are sadly mistaken. As you pass the gates you will observe a border force chap in a small elevated booth ... if you glance through the window you will notic he has a couple of monitors, where each persons camera is presented alongside the photo from their passport, if he like the look of you, a click of the mouse is all that is needed to let you through.
I really wish it was more sophisticated than that, but truly, it isn't.