Prime Minister Malcolm Turnbull says discussions with his British counterpart Theresa May over a possible free trade agreement have been constructive.

Key points: Turnbull says he is keen to take advantage of Britain's exit from the EU

Turnbull says he is keen to take advantage of Britain's exit from the EU May says she is also very keen to complete an agreement as soon as possible

May says she is also very keen to complete an agreement as soon as possible Vote to leave EU means Britain has to negotiate trade deals with Europe and other major markets

The pair have spoken for the first time since Ms May took over from David Cameron as British Prime Minister last week.

Mr Turnbull said he was keen to take advantage of Britain's exit from the European Union.

"Clearly our free trade arrangements with the United Kingdom of course are with the European community," he said.

"So as Britain leaves the EU, what we will need to do is negotiate direct arrangements with Britain ... we need to get moving on that quickly.

"Britain won't be out of the EU for several years — of course, that is the expectation at any event — but we need to get working on the new trade arrangements between Britain and Australia, as indeed Britain will need to undertake that work with many, many other countries."

While acknowledging that legal obligations prevent Britain from signing deals while still an EU member, Ms May said she was keen to complete an agreement as soon as possible, the statement said.

"I have been very clear that this government will make a success of our exit from the European Union," it quoted her as saying afterwards.

"One of the ways we will do this is by embracing the opportunities to strike free trade deals with our partners across the globe."

She added: "It is very encouraging that one of our closest international partners is already seeking to establish just such a deal."

Britain's June 23 vote to leave the European Union means the world's fifth-largest economy will have to negotiate new trade deals with Europe and other major markets in talks that could take years.

The European Commission hammers out trade deals on behalf of EU countries, meaning Britain has not negotiated its own deal since it joined the bloc in 1973.

Ms May has said she would not start the two-year process for Britain's exit from the EU this year and it is not clear when Britain could start new trade talks.

ABC/Reuters