In his final roll of the dice within the UK legal system, WikiLeaks founder Julian Assange claimed on Wednesday that the Swedish prosecutor who issued the European arrest warrant in December 2010 was not a proper judicial authority.
"This appeal involves a single issue of law which can be very simply stated. The question is whether a Swedish prosecutor has judicial authority for the purposes of the extradition act," Assange lawyer Dinah Rose told the court.
Seven judges are hearing Assange's appeal over two days at the court in London, which only deals with cases in which there is a wider public interest. They are not expected to deliver a judgement for several weeks.
Rose said it was not a "parochial" legal issue but a "pillar of natural justice" about the role of a judge, dating from the legal code set down by Byzantine Emperor Justinian 1,500 years ago.
There was no guarantee that a prosecutor would be as "independent and impartial" as a judge, Rose said, adding that allowing a prosecutor to issue warrants was "a serious interference with individual liberty."
Dozens of supporters gathered in bright winter sunshine outside the court and a peace activist sang "He shall be released" as Assange arrived.
In court, he sat flanked by his lawyers, including high-profile defence attorney Gareth Peirce.
Behind him was supporter Vaughan Smith, at whose mansion in eastern England Assange has spent most of the last year under virtual house arrest.
If the court rejects his appeal, the former computer hacker will have exhausted all his options in Britain, but he could still make a last-ditch appeal to the European Court of Human Rights (ECHR), prosecutors have said.
But if Assange wins his case, it could have serious implications for the European arrest warrant system, a fast-track extradition scheme for the continent.
Assange denies the rape and sexual assault allegations made by two women in Sweden, and still insists the sex was consensual. He has also claimed that the allegations against him are politically motivated.
WikiLeaks has enraged Washington by leaking thousands of classified US documents about the wars in Iraq and Afghanistan and Assange has said he fears he will eventually be handed over to the United States.
While the legal battle has dragged on, Assange's celebrity status has grown – he is to host his own TV show and will make an appearance as himself later this month on the 500th episode of the US cartoon show "The Simpsons."
Announcing the chat show, WikiLeaks described its founder as "one of the world's most recognisable revolutionary figures" and promised interviews with "key political players and thinkers."
So far, Russia's state-run RT is the only channel to confirm it would broadcast the show.
Assange's extradition to Sweden was initially approved by a lower court in February 2011. An appeal to the High Court was rejected in November, but he subsequently won permission to appeal to the Supreme Court.
If this appeal fails, the WikiLeaks founder will have only one other option to stop his extradition – an appeal to the ECHR in Strasbourg, France.
England's Crown Prosecution Service said in December that if the European court takes on the case, then Assange would remain in Britain under the same bail conditions until the case is resolved.
If the ECHR refuses, then he would be extradited to Sweden "as soon as arrangements can be made," England's state prosecutor said.
Julian Knowles, an extradition law specialist with the Matrix Chambers law firm, said the question of whether a public prosecutor was a valid judicial authority had been comprehensively tested by British law.