AFP - Swedish authorities on Thursday rejected arguments by WikiLeaks founder Julian Assange against his extradition, telling Britain's top court that if he won the case it could turn European law on its head.

The 40-year-old Australian -- making what is almost certainly his last appearance before British judges -- says the Swedish prosecutor who ordered his arrest in December 2010 over rape allegations was not a valid judicial authority.

But Clare Montgomery, the lawyer for the Swedish authorities, told the Supreme Court in London that at least eight countries would be barred from using the European Arrest Warrant (EAW) system if Assange's appeal were allowed.

"It would undermine the framework decision (of the EAW system) as it was agreed by, and as it has now been given effect by, a number of our extradition partners," Montgomery told the panel of seven judges.

She was speaking on the second and final day of the hearing at the wood-panelled courtroom in central London, after which the judges are expected to defer their decision for several weeks.

Assange is fighting extradition to Sweden to face allegations of rape and sexual assault made by two women, which he denies. He insists the sex was consensual and says the allegations are politically motivated.

If the Supreme Court rejects his appeal, Assange will have exhausted all his options in Britain but he could still make a last-ditch appeal to the European Court of Human Rights.

Dozens of supporters were again in court on Thursday to see the white-haired former hacker, who has become a cause celebre since his anti-secrecy website enraged Washington by leaking thousands of secret US documents.

In her arguments, Montgomery raised the legal systems of France, Denmark, the Netherlands and even Cambodia -- and there was laughter when one of the judges gently ribbed her after she tried to say "judicial authorities" in Dutch.

She added that there was "nothing either shocking to the conscience or violative of basic human rights" for a prosecutor or police officer to issue such a warrant.

But in her closing argument, Assange's lawyer Dinah Rose said Montgomery's case was "untenable".

On Wednesday, Rose had argued that extraditing him to Sweden would breach legal principles dating back 1,500 years and that only a judge or similar official should count as a proper "judicial authority."

Assange has spent most of the last year under bail conditions amounting to virtual house arrest at the mansion of a supporter in Norfolk, eastern England, although he recently moved out.

He has said he fears his extradition would eventually lead to his transfer the United States, where US soldier Bradley Manning is facing a court-martial over accusations that he handed documents to WikiLeaks.

While the legal battle has dragged on, Assange's celebrity status has grown.

He is to host his own TV show -- although Russia's state-run RT is the only channel to confirm it will broadcast it -- and will also make an appearance as himself this month on the 500th episode of the US cartoon show "The Simpsons".

A lower court in Britain initially approved Assange's extradition to Sweden in February 2011. An appeal to the High Court was rejected in November, but he subsequently won permission to appeal to the Supreme Court.