Julian Assange took his extradition battle to Britain's Supreme Court on Wednesday, arguing that sending him to Sweden would violate age-old legal tradition.

The two-day hearing is Assange's last chance to persuade British judges to quash efforts to send him to Scandinavia, where he is wanted on sex crimes allegations. The case will continue Thursday, but no decision is expected for several weeks.

Assange — who leads the WikiLeaks anti-secrecy website — was accused of rape, coercion and molestation following encounters with two Swedish women in August 2010, shortly after his group published sensitive U.S. government documents relating to the Afghan war.

He denies the allegations, claiming the sex was consensual.

Assange's case before the Supreme Court hinges on a single technicality: whether Sweden's public prosecutor could issue a warrant for Assange's arrest.

In Britain as in the United States, generally only judges can issue arrest warrants, and U.K. courts only honour European arrest warrants issued by what they describe as judicial authorities.

The warrant seeking Assange's arrest was issued by Sweden's public prosecutor, but British courts have so far upheld it on the grounds that Swedish prosecutors, like some of their European counterparts, play a quasi-judicial role.

Question of judicial authority

Assange lawyer Dinah Rose blasted that argument Wednesday, telling the seven justices gathered in the building's wood-panelled Courtoom One that a prosecutor "does not, and indeed cannot as a matter of principle, exercise judicial authority."

'No one may be a judge in their own case.' —Assange lawyer Dinah Rose

Rose said that putting the power to arrest suspects in the hands of the same prosecutors bent on trying and convicting them was completely unfair.

She said this is not a parochial British view but rather a venerable rule whose origins go back 1,500 years to the laws of the Byzantine Empire.

"No one may be a judge in their own case," Rose said, calling it "about as fundamental a principle as you can have."

Rose spent the next four hours combing through British case law and parsing European draft treaties to buttress her case — sometimes even slipping into French to make finer points about the documents' wording.

Evidence showed, she said, that drafters believed "that the European arrest warrant was a very serious measure that has to be issued by a court."

She went on to attack the European arrest-warrant system, saying that countries across Europe implemented it in problematic ways, and criticized Sweden's justice system, which she said had failed to fulfil its obligations.

Impartiality and arrest warrants

Rose spoke confidently and with few interruptions — unlike Sweden's lawyer Clare Montgomery, who was repeatedly questioned by judges about her assertion that impartiality wasn't a prerequisite for issues involving arrest warrants.

"The decision whether to arrest somebody might be made by somebody who is partisan," she insisted. "That happens throughout Europe."

Experts interviewed before the hearing said the advantage was with Montgomery and Swedish authorities.

Karen Todner, a prominent extradition specialist, said that Assange's lawyers were unlikely to overcome the benefit of the doubt usually afforded to other European countries' judicial systems.

British judges "absolutely defer" to their European counterparts' justice systems, she said, adding that she would be "very surprised" if Assange's team triumphed.

The U.K. justices, who have dispensed with formal court attire in favour of business suits, will hear lawyers for the prosecution on Thursday.

If they rule against Assange, the 40-year-old Australian is expected to be on a flight to Sweden within two weeks. Assange could conceivably appeal to the European Court of Human Rights, but because Sweden is a fellow European country that would not stop his extradition.

Once in Sweden he would be arrested and a detention hearing would be held within four days. Prosecutors could decide to release him after questioning, but the court could also extend his period of detention. Such hearings must be held every two weeks until a suspect is charged or released. There is no bail in Sweden.

It's still not clear whether charges will be brought against him in Sweden. If Assange is convicted, the penalties for the types of crime he's accused of range from fines to as much as six years in prison.