WikiLeaks founder Julian Assange today took one crucial step closer to extradition as the UK Supreme Court ruled that Sweden's European Arrest Warrant (EAW) for his capture and return was in fact valid.

Assange has been in England since December 2010, when the Swedish arrest warrant was issued by a state prosecutor there. It came after complaints about sexual molestation and rape were lodged against Assange, who had already left the country. Assange has been under house arrest (and subject to electronic monitoring) in the UK ever since as he fought the Swedish extradition request.

His case reached the UK Supreme Court, which heard arguments that the EAW was invalid because it had not been issued by a "judicial authority," as required by the UK's 2003 Extradition Act. Assange's lawyer argued that a Swedish prosecutor was not an impartial judge, and that such warrants should be valid only when issued by a member of the judiciary. The situation was murky—an early draft of the European Union "framework decision" that formed the basis for the Extradition Act had once mentioned "prosecutors" explicitly when talking about warrants, but this was removed in the final copy. At least 11 European countries did name prosecutors as "judicial authorities" when it came time to implement the framework in national law—but the Extradition Act did not mention them.

Two Supreme Court judges, Lord Mance and Lady Hale, sided with Assange on the question of the warrant's validity. According a summary of the court's decision, Lord Mance argued that the Court was bound by what Parliament had actually written and enacted; as a guide to interpretation, he also noted that cabinet ministers' statements "showed that repeated assurances were given that an issuing judicial authority would have to be a court, judge or magistrate." Lady Hale agreed "that the Supreme Court should not construe a UK statute contrary both to its natural meaning and to the evidence of what Parliament thought it was doing at the time."

But the other five judges found the Extradition Act ambiguous and so interpreted it in a way that would not put Britain in breach of its international obligations. They ruled that Assange should in fact be sent to Sweden, but not before granted him one more chance to convince them otherwise. Assange's lawyer was given 14 days to file an appeal on grounds that the Court made its decision using legal principles that had not been argued over in the case.

Should Assange eventually be extradited, he will still face a full trial in Sweden to determine guilt or innocence; the current arrest warrant is merely a request to return him to Swedish jurisdiction for legal proceedings.

The WikiLeaks Twitter account has been writing widely about the decision this morning, and has already conjured a link between US government policy, Sweden, and the decision. "Hiliary Clinton [sic] and State Dept team arrive Stockhom [sic] June 3-4; 4 days after Assange extradition decision. Fanciful to think no discussion," WikiLeaks wrote. Assange has long claimed that the Swedish prosecution is a politically motivated tool to get him to Sweden, and from there sent on to the US. Leaked e-mails from StratFor, which was hacked by members of Anonymous, suggest that the US has laid the groundwork for a case against Assange.

If you want to read more than you ever thought it possible to say about European Arrest Warrants, the UK Supreme Court has made its decision available online.