WikiLeaks founder Julian Assange has asked the Supreme Court to block his extradition to Sweden on the grounds that the European arrest warrant issued against him is "invalid and unenforceable".
A QC for the 40-year-old Australian said the Swedish public prosecutor who signed the warrant could not issue a valid document because she lacked "impartiality and independence".
Assange, who is on bail living with friends, was at the UK's highest court in person for his latest attempt to block his removal to face questioning on sex crime allegations.
He is appealing against a High Court ruling that it would not be unfair or unlawful to extradite him.
The Swedish authorities want him to answer accusations of "raping" one woman and "sexually molesting and coercing" another in Stockholm in August 2010 while on a visit to give a lecture.
Earlier, dozens of supporters gathered outside the court as the Australian began his challenge before seven judges. He is attempting to overturn a High Court ruling that it would not be unfair or unlawful to remove him.
Assange, whose WikiLeaks website published a mass of leaked diplomatic cables that embarrassed several governments and international businesses, says the sex was consensual and the allegations against him were politically motivated.
Dinah Rose QC, for Assange, told the judges that today's appeal raised the single issue of law as to whether the Swedish public prosecutor constituted a "judicial authority" capable of issuing a valid warrant under the provisions of the 2003 Extradition Act.
It was common ground that if she did not, "there is no legal basis for the extradition of Mr Assange to Sweden".
Ms Rose suggested it was "obvious" that a public prosecutor whose function it was to investigate and prosecute an individual "cannot exercise judicial authority in relation to that individual".
As "a matter of fundamental legal principle dating back hundreds of years" a judicial authority had to be impartial and independent both of the executive and the parties in a case.
"Since the Swedish prosecutor cannot fulfil those conditions, she is not a judicial authority and not capable of issuing a warrant for the purposes of the 2003 Extradition Act," she said.
She was breaching the principle that "no-one may be a judge in their own cause", Ms Rose added.
Assange is due to host a TV programme, broadcast on Russian RT station which on the Wikileaks website says will feature "in-depth conversations with key political players, thinkers and revolutionaries" from around the world.
The Wikileaks founder has also agreed to take part in a vocal cameo in The Simpsons 500th episode, which will see Marge and Homer bump into Assange after being exiled from Springfield.
Assange is fighting a ruling made in the High Court by District Judge Howard Riddle at Belmarsh Magistrates' Court, south London, that the computer expert should be extradited to face investigation.
The whistleblower website, which claimed a database of 1.2 million documents within a year of its 2006 launch, regularly hit the headlines in 2010 with a series of leaks.
The US Embassy Cables, Afghanistan war logs and Iraq war logs, which were drip-fed to the media in 2010, helped raise his profile.
If the Supreme Court rejects his appeal it will mark the end of his lengthy legal battle in the UK, but it will still be open to him to ask the European Court of Human Rights in Strasbourg to intervene on his behalf.