WikiLeaks founder Julian Assange is appearing before the Supreme Court as his fight against extradition to Sweden, where he faces allegation of sex crimes, enters its final stage.
Dozens of supporters gathered outside the court on Wednesday morning as the 40-year-old 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.
This is his last chance to contest the ruling, after a lengthy legal battle which started with his arrest in December 2010.
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.
A key legal question before the Supreme Court justices is whether a European Arrest Warrant (EAW) issued against him by a Swedish public prosecutor is valid under provisions of the 2003 Extradition Act.
Dinah Rose QC, appearing for Assange, told the judges the appeal raised a "significant issue of law." She claimed that the Swedish prosecutor who issued the European Arrest Warrant against Assange was not independent or impartial and therefore the arrest warrant was invalid.
Rose argued that the Swedish prosecutor constituted "a judicial authority" for the purposes of the 2003 Extradition Act and that because the Swedish prosecutor was herself a party in the Assange case she breached the principle that "no-one should be judge in their own cause".
The issuing of a warrant constituted "a serious interference with individual liberty".
Ms Rose submitted: "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 he 2003 Act." The arrest warrant was therefore invalid.
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 are politically motivated.
Julian Assange has become a minor celebrity after bursting into the public consciousness in April 2010 when Wikileaks released Collateral Murder - video footage of a US air crew shooting Iraqi civilians in 2007.
Upon his arrest in December 2010 he had a number of famous friends and supporters who helped him to raise bail of £200,000.
These included film-maker Ken Loach and socialite and charity fundraiser Jemima Khan, who each offered £20,000.
He has been on bail and living at the country mansion of a wealthy supporter in Norfolk
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.