What is the origin of the Australian slang “pommers” to refer to English people?

Question

What is the origin of the Australian slang “pommers” to refer to English people?

(I’m uncertain as to the spelling)

Why is this the term that is used?

Answer 1

It's one of the many variants built off of the early-twentieth-century pommy.

From The New Partridge Dictionary of Slang and Unconventional English:

Pommy; Pommie noun

an English person, or more loosely, a person from Britain [AUSTRALIA, 1912] Originally used of English immigrants to Australia, it is a shortening of the now obsolete 'Pomegranate', rhyming slang for 'immigrant'. The rhyming slang term and the shortened variants 'Pom' and 'Pommy' all appear in the lexical record at the same time. The occasional spelling 'pommygrant' shows the rhyming pronunciation. Although this word carries a definite negative connotation, it also can be used as a term of affectionate abuse (see POMMY BASTARD and WHINGEING POM). The suggestion that Pommy is actually a respelling of P.O.M.E., standing for the reputed term Prisoner Of Mother England, or P.O.H.M.I.E, standing for Prisoner Of Her Majesty In Exile, and other variations on this theme, are implausible on phonetic grounds and are in themselves anachronistic as acronyms were not a common feature of English in the early part of C20.

POMMY - English immigrant. [Gilbert H. Lawson, A Dictionary of Australian Words and Terms, 1924]

All pommies are bastards, bastards or worse. / And England is the arsehole of the universe. [The Adventures of Barry McKenzie, 1972]

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From 1923, in The Albury Banner and Wodonga Express:

The word 'pommy,' as applied to newcomers from the old-land, is still causing a mild sensation as to its origin, or derivation, in several papers. When the writer was gaining experience 'down the river' at Wilga Station, with a pick and shovel, immigrants were facetiously called 'jimmygrants.' Up in Queensland, where the pomegranate grows, the term was altered to 'pommygrants,' hence 'pommie'. Pomegranate and immigrant and 'Jimmygrant' were evidently considered semi-synonymous terms by the small-minded fry, who can see no good in a stranger. But, really, it is much ado about nothing.

Here is a 1900 use from The Sydney Morning Herald in a feature called At Ladysmith: How Sniping is Done:

They were being shown the little one's pet rabbits, when another splinter of shell passed within a couple of feet of them and then one of the rabbits in twain. A thoughtful Pommy took it to his tent for a stew.

Answer 2

Wikipedia has a list of Australian slang words for people, and says:

pom or *pommie - an Australian nickname given to English people. Somewhat derogatory in nature the term can be used in both a positive and negative context. There is a debate as to how the word came about, some believe the original term "POME" is an anacronym for "Prisoner Of Mother England" the title given to convicts sent to the early Australian penal colonies. In a reverse of circumstances Australian's joke that it is the English who are now the prisoners in their own country (mother england) as the Australian lifestyle is widely regarded as better than England's. The other is the English have round rosey cheeks similar in resemblance to a pomegranate.