On The Origin Of The Australian Term, "Pom" or "Pommie"

I've heard many origins of the word Pom / Pommie as given in affection and insult to someone from the UK, especially to the English* You may have heard of Prisoner Of [his] Majesty. I'm reading The Word Detective: Searching for the Meaning of It All at the Oxford English Dictionary by former OED editor John Simpson and he states the following convoluted path:

* I suspect it was those from "the UK" but back were, and still are, called "English" or "from England" by Australians and Kiwis. The use of the word "Pom" has changed since I've been in the southern hemisphere and is much more connected specifically with English as highlighted by how people apologise when I tell them I'm  actually from Wales.