Fun fact: the passport gates at UK airports appear to be biometric, but aren't. You step into a little gate, place your passport photo page down onto a scanner, and look into a camera for a photograph.
The thing which slows folks down at passport gates (and the reason the best passport control agents don't have a jocular welcoming patter) is the hello/goodbye/talking around the manual "look at your face, look at your passport".
When the gates open at Heathrow and you're allowed through, you'll immediately see a raised bank of desks behind which sit a bunch of officer who are simply manually verifying that the person in the photo appears to be the person on the passport.
I did some digging to make sure that isn't what's happening here (all the articles seem to be very vague about the "biometric" and "facial recognition" part). Here's where I got to:
> Using facial recognition, TVS enables biometric identity verification by transmitting automated queries to locate photos in DHS and U.S. Department of State databases for matching against the unique characteristics of a traveler’s facial features. As designed, this updated capability operates in a virtual, cloud-based infrastructure that can store images temporarily and operate using a wireless network, thereby eliminating the need for the tablets previously used in 2016.[1]
[1] https://www.oig.dhs.gov/sites/default/files/assets/2018-09/O...