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.
Some of his supporters had been queueing since 5.45am to attend the two-day hearing before a panel of seven judges.
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.
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.
Clare Montgomery QC, for the Swedish Prosecution Authority, urged the judges - Lord Phillips, Lord Walker, Lady Hale, Lord Brown, Lord Mance, Lord Kerr and Lord Dyson - to reject the Assange appeal.
She argued that the High Court was plainly correct to accept that the term "judicial authority" had a wide and autonomous meaning, and it was not restricted in the way contended for by Ms Rose.
When the European arrest warrant (EAW) framework was set up, the drafters had intended it to include the prosecutors of many countries, submitted Ms Montgomery.
This "broader approach" recognised the "historic role" of public prosecutors within EU member states in authorising arrests and making extradition requests.
She said in her written submissions that the principle of "mutual recognition" underpinning EU efforts to achieve co-operation between member states "requires the UK to recognise and act on EAWs issued by those identified as 'judicial authorities' under the domestic law of the issuing state".
She added: "Since the start of the EAW scheme it has been the practice of a number of prominent member states to issue EAWs through public prosecutors.
"There is no conceivable breach of fundamental rights involved in such a process."
The hearing continues tomorrow.