Malcolm Turnbull has been taken to task by a British Tory MP over his support for the UK remaining in the European Union.
Conservative MP Andrew Rosindell says it's "nonsense" for the prime minister to want Britain to remain in the EU, saying Australia would never join a political union with its Asian neighbours like the UK has in Europe.
"Australia would never countenance signing away permanent legal power over its rules, its laws, its traditions to other countries in the Asia Pacific region," he told ABC radio.
The attack comes weeks after Mr Turnbull declared that while Britain's EU membership was a matter for Britons, Australia would welcome the UK remaining one of the 28-member countries.
Mr Turnbull stood by his comments on Wednesday, saying he is on a "unity ticket" with US President Barack Obama and the prime ministers of Canada and New Zealand in supporting Britain being part of the EU because of the benefits membership brings.
"It is to our advantage if Britain is part of the EU. They are part of a big market and they're a good friend to have there," Mr Turnbull told reporters.
Mr Turnbull was dragged into the heated debate over the future of Britain's EU membership exactly four weeks before a referendum is held to decide the issue on June 23.
Mr Rosindell argues that remaining an EU member disadvantages Australians wanting to work in Britain.
Australians and other non-EU residents have been subject to a recent visa crackdown, while EU residents can move to its shores visa-free.
Mr Rosindell said Britain should develop closer ties with countries like Australia, New Zealand and Canada and allow freer movement between them.
"Why should we treat Australians as second-class citizens in Britain?" he said.
Annmarie Elijah, associate director at the Australian National University's Centre for European Studies, says a "Brexit" could put preliminary free trade talks Australia is having with the EU on the backburner, and it could have to start separate talks with Britain.
"From a government position, they will try to make it business as usual but Australian businesses will have an uncertain environment," Dr Elijah told AAP.
Australian British Chamber of Commerce chief executive David McCredie says a recent poll of its members found 54 per cent favoured Britain remaining in the EU.
"There are so many risks around leaving and no guarantee of an upside to going," he said.
Mr McCredie said about 2000 companies transact daily between Australia and Britain, with many Aussie businesses having benefited from using the UK as a base to do business in the EU.
He said it could take at least two years for Britain to exit the EU, creating plenty of uncertainty for businesses which would be left in "limbo".
AUSTRALIA'S EURO TIES:
* The EU is Australia's second largest trading partner, largest source of foreign investment ($958.97 billion)
* The UK is Australia's second largest source of foreign investment ($484.1 billion)
* About 5.2 per cent of Australians were born in the UK.