What does the phrase "High Numbers" have to do with the Modernists of 1960s England?

My Rock History textbook notes that the Who were originally called the High Numbers as an acknowledgement of their solidarity with the Modernist (or Mod) movement. What on earth is the connection? Why is “The High Numbers” more Mod than “The Who”? The same book also notes that the Who eventually decided to change their name out of fear that “The High Numbers” would become dated with the passing of the Mod movement. Apparently, everyone and their mother would’ve associated the words “High Numbers” with Mod culture. Why?

I can find a couple of brief explanations, but nothing definitive; all bolding in quotes below is mine.

From here:

This is supported here:

An alternate explanation is here:

I’m sure someone will come alonfg with better cites than the above.

Very interesting. Thanks!

Any other theories to be found?

Sorry, no cite here, but my understanding was that in Mod terminology, “number” might be roughly equivalent to today’s “poser/poseur”, in that a number was someone who looked/dressed like a Mod, but wasn’t really a true Mod. I think I heard this as an explanation of what The Jam’s “Away From The Numbers” is supposed to be about.

If true, I’m not sure why The High Numbers would want to call themselves that, though. Maybe it was supposed to ironic or something. Or maybe “number” had taken on a new meaning by the time The Jam came about.