This Englishman has never heard of London broil, either. The name means nothing to me and upon Googling it, I’ve never seen it under a different name, either. We don’t even use the cooking term “broil” in the UK - we say “grill”.
The little bit of research I’ve done shows the name’s origin is lost in the mists of time, but perhaps refers to London Ontario.
I once unintentionally duplicated this experiment in an unobserved toaster and the resulting Pop-Tart conflagration nearly burned down my kitchen.*
*Okay, that’s hyperbole, but you don’t want to walk into your kitch with two feet of flames shooting up from the toaster slot. That’s scary!