One of Sweden's most senior legal figures has offered public support for Julian Assange, saying the WikiLeaks founder should not be punished for exposing confidential information.

Mr Assange is wanted in Sweden for questioning over sexual assault allegations.

He has been holed up at Ecuador's London embassy since June, fearing he could be extradited to the United States to face conspiracy charges for leaking classified military documents.

The Swedish government has spent more than 3 million British pounds on surveillance at the embassy in case Mr Assange tries to flee.

The activist's legal team has said the Swedish case is a "holding case" ahead of extradition to the US.

But Swedish Supreme Court chairman Justice Stefan Lindskog says Mr Assange may be safe from extradition even if he returns to Sweden.

Mr Lindskog says his country's laws protect those wanted in other countries on political charges.

"Extradition is permitted provided the offence for which extradition is requested is equivalent to a crime punishable under Swedish law," he said in a public lecture at the University of Adelaide last night.

"Thus, extradition requires, firstly, an offence punishable under the law of both countries - dual criminality.

"But there are also other restrictions. Extradition may not be granted for military or political offences.

"Nor may extradition be granted if there is reason to fear the person whose extradition is requested runs the risk of being subjected to persecution.

"Does Assange face a risk of being extradited?

"I don't know what crime if any Assange's involvement in the publishing of military and diplomatic documents would amount as regards the law of the United States.

"I have however read that Assange may be charged for communicating national defence information to an unauthorised source and aiding the enemy. As I understand it, it is about espionage or treason.

"That raises some interesting questions. The first question is, do we have an equivalent criminalisation in Sweden? Yes of course.

"But I think the question should rather be put in this way: is the offence for which extradition is requested a crime under Swedish law? That could be debated.

"What is classified under US law is probably not classified under Swedish law. Enemies to the US may not be enemies to Sweden."

'Benefit of mankind'

Justice Lindskog says the actions of Wikileaks and MrAssange have been good for society and, for moral reasons as well as legal, should not be punished.

"He will be thought of person who made public some pieces of classified information to the benefit of mankind," he said.

"The good made by leakages of such information cannot be underestimated.

"In my opinion, a state that claims to have been offended and therefore applies for extradition of the purported persecutor shall not be helped out.

"It should never be a crime to make known crime of a state.

"I strongly hold that the part of leakage was good for society and should not be punished."

He says Swedish authorities should consider questioning Mr Assange in London.

But John Keane, a professor of politics at Sydney University, says the threat of extradition to Mr Assange remains strong.

"Last year, Sweden passed a new espionage law that quite probably contain or prepares the way for an extradition," he said.