The four-minute film features Mr Downer strolling through Australia House and is set to an acoustic version of Waltzing Matilda and finishes with Mr Downer being chauffeured through central London in a Jaguar car with the numberplate "AUS1."

He begins by reflecting on his own father's career as a High Commissioner to London in the 1970s, when Britain was joining the body which would become the EU as it is known today.

"Now I'm in the job, the UK is leaving," Mr Downer observes.

"Now that the decision has been made we hope that Britain will get on with the process of negotiating their exit from the European Union and making the most of the opportunities that are presented to it," he said.

His television appearance followed an opinion piece published in Britain's Telegraph newspaper in which he argued Australia was hurt by Britain's decision to turn its back on the Commonwealth in favour of the EU back in the seventies.

Australia's formally opposed Britain leaving the European Union but since Britain's decision to leave the EU, leading figures, including Mr Downer and former Prime Minister Tony Abbott have eagerly spruiked the benefits for Australia and Britain.

Mr Downer said one of those opportunities would be a free-trade agreement (FTA) with Australia. Scoping talks have already begun but Britain is not allowed to formally begin negotiating any FTAs until it formally leaves the EU, under EU rules.

Trade Minister Steve Ciobo has previously told Fairfax Media the government is prioritising its trade negotiations with the European Union ahead of any deal with Britain. He says talks with the UK are at a "juvenile stage."

But Mr Downer said an Australia-Britain deal would take no time at all to conclude.

"It's not as hard as some people say. We may have preferred the UK remain in the EU but life outside as we know can be pretty good."

"We've negotiated eight FTAs over the last twelve years, including an FTA with the United States which took us 15 months."

In an interview broadcast after the "exclusive film," Mr Downer conceded that Australia had been forced to give up hopes of Australian sugarcane growers accessing the lucrative US market, because of American domestic pressures.

"There was one sector the Americans insisted on protecting and that was their sugar industry...we had to answer the question would we go ahead with this FTA without sugar and we decided we would do that."

"I don't think a free trade agreement would take very long to negotiate with the UK because the UK wouldn't want to put a lot of obstacles in the way of Australia," Mr Downer said.

Mr Downer appeared to rule out free movement for Britons and Australians once Britain has left the European Union.

"Probably not," Mr Downer said, when asked if a British-Australia FTA could lead to free movement for each country's citizens.

This is at odds with calls made by former Prime Minister Tony Abbott who is calling for such a zone to be established.

Mr Downer's media appearances were applauded by one of the Leave campaign's most prominent voices - the Tory member of the European Parliament Daniel Hannan.

"Thanks mate," Mr Downer tweeted back.

The British government is unclear about when it will formally leave the European Union although Prime Minister Theresa May says she will formally trigger Article 50 by April next year. This gives the British government at least two years to negotiate its exit.

However there have been calls, including from the Chancellor of the Excheqeur Philip Hammond, for a transition arrangement which could see Britain remaining inside the customs union for longer.

The British government is keeping tight-lipped about how it plans to leave the EU and whether or not it will compromise on key issues like free movement and the single market.

Liam Fox, UK international trade secretary. Photo: Bloomberg

Britain's Secretary for International Trade Liam Fox suggested the UK could remain inside the customs union, in significant comments given he is an arch-free trader and campaigned for Brexit.

If Britain does stay in the customs union it would restrict it from negotiating new FTAs.

"There would be limitations on what we could do in terms of tariff setting which would limit what kind of deals you would do, that's quite correct but we want to look at all the different things," he said.

"Turkey for example is in part of the customs union but not in other parts," he said.

"We can't go for a quick result we have to get the right result," he told the BBC.

George Osborne. Photo: Simon Dawson

Former Chancellor George Osborne told the BBC's Andrew Marr show that no red lines in Britain's negotiations with the EU, other than that Britain should leave in accordance with the people's wishes.

"I would not go into this negotiation necessarily drawing red lines," he said.

"I would say we are leaving the EU - that's the only red line I would draw - let's go in there and try and get the best deal for Britain."

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