A vote by Britain to split from its European partners is likely to send ripples all the way Down Under.
After months of heated debate, Britons will vote in a once-in-a-generation referendum on Thursday on whether to remain within the 28-member European Union or leave.
While the "leave" and "remain" campaigns are neck-and-neck in the polls, Australian businesses and those wanting work or student visas may be affected over the medium-to-long term if the vote favours a so-called "Brexit".
Australian British Chamber of Commerce chief executive David McCredie says Aussie businesses with operations in the UK and EU could face two years of uncertainty as the pair unwind treaties and negotiate ground rules for their future.
"It's not like if they vote to leave on Thursday that the UK will be out on Monday," he told AAP.
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"For organisations that use the UK as a landing pad for operations in Europe there will be uncertainty about their continental and Irish connectivity and treatment."
A potential upside could come from Britain, the world's fifth largest economy, being free to negotiate a trade deal with Australia.
That could open the door to lower tariffs on Australian exports, making them more attractive price-wise compared to global rivals.
Conservative think tank The Institute of Public Affairs expects Australia and Britain could seal a deal quickly.
"For Australia there would be significant opportunities for our high quality agriculture exports in the UK market," the institute's adjunct fellow, Georgina Downer, wrote in a research paper in support of Brexit.
Aussie wine is currently slapped with an extra tariff in the UK while EU plonk is tariff free.
Wine Australia's regulatory services head Steve Guy isn't convinced Brexit would automatically mean an end to tariffs for Aussie winemakers, but the playing field could be levelled.
"Those countries that aren't subject to a tariff suddenly could be," he said.
While the UK and Australia would be free to discuss trade, preliminary free trade agreement talks between Canberra and the EU scheduled for January 2017 could be delayed.
Annmarie Elijah, associate director at the ANU Centre for European Studies, says a Brexit would probably mean the EU having to focus on trade issues with Britain rather than Australia.
"All bets could be off," she said.
However, Brexit could make it easier for Australian students and workers to obtain UK visas.
Leave campaigners argue Britain would be able to control how many EU citizens move to its shores if it splits from the EU.
Immigration has been a hot topic during the referendum debate amid concerns about the influx of EU citizens to Britain, which has in response restricted the numbers of Australians and others wanting to work and study there.
But Mr McCredie warns any changes to Britain's visa system could take years.
He also notes warnings by economists about a possible British recession if there is a Brexit.
"That doesn't bode well for Australians who want to suddenly uproot and move to the UK," he said.
TIES BETWEEN AUST AND BRITAIN
* Britain is Australia's seventh largest two-way trading partner and leading EU trading partner
* Two-way trade was $21.1b in 2014/15
* About 2000 companies transact daily between Aust and Britain
* Gold, alcohol and lead are Australia's major exports to Britain
* Cars, medication and printed material are Britain's major exports to Aust
(Sources: DFAT, Australian-British Chamber of Commerce)
