After 18 months of living under partial house arrest, WikiLeaks founder Julian Assange on Wednesday again staved off extradition to Sweden, where he is wanted for questioning over alleged sex crimes.

At a brief hearing in central London, Britain’s Supreme Court denied Assange’s appeal against extradition but in a new twist allowed his legal team the chance to contest its ruling.

The court’s president, Nicholas Phillips, told the packed courtroom that in a 5 to 2 decision, the justices had dismissed Assange’s argument that a European arrest warrant issued for his extradition was flawed.

The judgment had been billed as the final leg in Assange’s marathon legal battle in British courts, but instead the court granted Assange’s attorney, Dinah Rose, 14 days to consider lodging an application to reopen the case after she argued that the justices’ decision was based on a point not discussed during the hearing.

It was the first time the court has said it would accept a challenge to one of its rulings since it began work in 2009.

Britain’s Crown Prosecution Service has agreed not to deport Assange before June 13, and even then, he can still appeal to the European Court of Human Rights in Strasbourg, France, which would have two weeks to decide whether or not to take the case.

Assange, 40, is wanted for questioning in Sweden about separate encounters he had with two WikiLeaks volunteers during a visit he made to Stockholm in August 2010. Although he admits to brief affairs with the women, he adamantly denies their accusations of rape, sexual assault and unlawful coercion.

In February 2011, a lower court in Britain ruled that he should return to Sweden to face questioning. Assange appealed that ruling and lost, but he won permission to appeal to the Supreme Court, which agreed to hear the case before seven judges — two more than normal — because, the court said, of the “great public importance of the issue raised.”

The case before the court had nothing to do with the sex crime allegations but rather hinged on a technicality. Assange argued the European arrest warrant that triggered his arrest in December 2010 was invalid because it was made by a prosecutor rather than a court or a judge.

Under the European extradition treaty, ushered in to help speed up transfers between European nations, a “judicial authority” must issue the warrant.

In a 161-page judgment, the Supreme Court said that a judicial authority could mean a prosecutor, as indeed it does in many European countries.

Assange’s team is now focusing on another narrow point. They contend that the majority of the seven justices on the panel based their reasoning largely on their interpretation of the Vienna Convention on the Law of Treaties — a point that lawyers did not have a chance to discuss during the appeal.

Assange shot to international fame when his anti-secrecy Web site leaked official state secrets in the form of hundreds of thousands of Afghanistan and Iraq military reports and diplomatic cables.

His supporters say the allegations lodged against him are politically motivated and that Swedish authorities might hand him over to the United States, where he could face charges over leaking national secrets.

Over the next two weeks, Assange will remain in Britain under his current bail terms, which include wearing an electronic tag around his ankle and checking in daily with local police.

Unusually for him, Assange was not at the court hearing Wednesday. His lawyers told reporters that he was stuck in traffic.