Australian slang term for attacks on the English.
The word 'pommy' derives from pomegranate. The English were called Limeys because they ate limes to ward off scurvy on the long sea voyage, but the pomegranate tag didn't originate that way. Pommy grant is likely to have originated as a form of rhyming slang for immigrant.
Popular myth has it that pom derives from the fact that many immigrants to Oz were British convicts who had been transported there. They supposedly arrived with POHM (Prisoner of Her Majesty) printed on their clothes. Like most phrases that are supposed to derive from acronyms, that notion is supported by no evidence whatsoever.
The terms pom and pommy began to be used in Australia just before WWI and the first known citations of it in print date from 1912 and 1913 respectively.
In the UK in 1970s a vogue arose for calling racial assaults on Pakistani immigrants 'Paki bashing'. This originated from the frequent such assaults made by the far-right racist party the National Front. The first record I can find for this is from The Times, April 1970:
"'Paki-bashing', as skinheads call it, is not confined to east London."
The term 'pommy-bashing' was coined following this pattern, although there the victims suffered only mild abuse, sometimes just teasing, rather than physical attack. This was cited in The Times in April 1976:
"'Pommy-bashing' vogue which achieved undeserved notoriety last year."