I’d always thought it was Australian, but turns out it’s English. Here is a telling of the origin of the phrase. It came after a 2005 invasion of the International Petroleum Exchange trading floor in London. This is the key moment but the entire article bears reading through:
The trespassers were set upon by traders, most of whom were under the age of 25. “They were kicking and punching men and women,” said a photographer, according to The Times of London. “It was really ugly. … They followed the [Greenpeace] guys into the lobby and kept kicking and punching them there. They literally kicked them on to the pavement.”
“The violence was instant,” reported one aggrieved recipient of a rain of blows to the head. “I’ve never seen anyone less amenable to listening to our point of view.”
“Sod off, Swampy!” shouted one tardy trader, steadying himself against the railings of the balcony of the pub across the street as his colleagues threw the protesters bodily onto the sidewalk. (Swampy was an enviro-protester who gained fame by living unbathed in a tunnel for eight months.)
But here is the Australian connection: ‘I understand that some enterprising manufacturer in Australia is already making “Sod off, Swampy!” T-shirts’. I hope he sold a million.
UPDATE: This has now been added to the comments thread at Instapundit so it may yet be an Australianism after all:
I heard Sod Off Swampy decades ago on Crocodile Dundee, so I have doubts about the origin of the expression given in the article.