More has emerged about a little-known French proposal to invade the British colony at Sydney Cove more than two centuries ago.

Historians have often speculated that until Nelson defeated Napoleon's navy at the Battle of Trafalgar in 1805, France had plans to invade Sydney.

Now researchers from Adelaide University say they have proof.

For the first time they have translated into English a confidential report from one of the explorers on the Nicholas Baudin expedition of the early 1800s.

Francois Peron, the chief zoologist and intellectual leader of the expedition, authored the draft report in 1802, 14 years after Port Jackson was established.

But until now, only sections have been translated into English.

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Associate Professor John West-Sooby heads the Discipline of French Studies at Adelaide University and went to France to see the document.

He says the full translation adds weight to the argument that Port Jackson was a strategic location rather than just a convenient place to dump convicts.

The full document shows the French considered destroying the colony, but Peron instead recommended keeping it because they could use it.

"It's a mix of Anglophilia and Anglophobia; he describes in really glowing terms what the English have achieved, but he's also outraged at this kind of unilateral decision to annexe this vast part of the world for themselves without consulting Europe," Associate Professor West-Sooby said.

"The language is quite colourful, talks about their 'outrageous encroachments' and 'this outrageous act of possession' and so on and so forth.

"And (it) explains England is about to settle in Tasmania because they don't want to have such dangerous rivals as the French as their neighbours and so on and so forth.

"So it's pretty racy read."

Anxious

The study stems from a larger research project with the University of Sydney to translate other Baudin expedition documents.

Margaret Sankey from the University of Sydney has been involved in that project, and says Peron's document sheds new light on the sea voyage between 1800 and 1804.

"He thought that the Irish, because they were sort of disaffected with the English, and the Aborigines might side with the French and plan this possible invasion, but really there's no evidence from any other sources," she said.

"Nevertheless, the idea of whatever Peron had said to various people during the stay of the expedition in Port Jackson, Governor King became quite anxious after everybody - the ships, French ships left in November 1802 and sent a ship to King Island to make sure to plant - put the French, the Australian flag on King Island because he thought the French might be contemplating some sort of land grab."

Professor Sankey says she does not know why it has taken so long to unearth the details.

"We would hope it would become much better known because, in fact, the Baudin journey doesn't seem to be given, in Australian history, it's not given the credit that it deserves," she said.

"Because Australian history, as we know, is mainly Anglo history, and really the Baudin expedition did a lot of scientific work, discovered a lot of species of plants, new species of plants and animals."

The news nevertheless is causing excitement in historical circles.

'Secret agent'

"It would be fascinating to know the actual turn of phrase, how he expressed it, you know, in the English language to get that feeling of just how strong his views were," said Murray Radcliffe, vice president of the City of Sydney Historical Association.

"The leader of the expedition was a scientist and he had no sort of political ambitions, but this guy, Peron, was sort of buried in the fleet and was like the political or secret agent that was feeding political and military information back to France.

"Maybe the leader would never have sanctioned that."

The Adelaide researchers are planning to publish the full text of the document online and in a book to be published next year.