(Reuters) - WikiLeaks founder Julian Assange, who is fighting extradition to Sweden, won the right on Monday to ask Britain's Supreme Court to hear his case, prolonging his stay in Britain.

Swedish authorities want to question the 40-year-old Australian over accusations of rape and sexual assault made by two female former WikiLeaks volunteers in August 2010.

Assange, who has been living in Britain since his arrest here in December last year, denies wrongdoing.

Monday, two High Court judges ruled that he could ask the Supreme Court to look at his case. However, the ruling does not guarantee him a hearing. The Supreme Court, Britain's highest, can decide to hear his case, or reject his petition.

Assange now has 14 days in which to formally lodge an appeal, meaning his stay in Britain is certain to stretch into 2012.

Asked by Reuters as he left the court if he thought the ruling was a victory, the silver-haired Assange said Yes before he was whisked away through a crowd of reporters and supporters.

Dressed in a dark grey suit, Assange embraced his lawyer Gareth Peirce after the hearing in London.

The two judges ruled that Assange's case raised a question of general public importance that should be decided by the Supreme Court as quickly as possible.

Assange argues that the European arrest warrant on which he is being held is invalid because it was issued by a prosecutor in Sweden rather than by a court or a judge.

I am a bit surprised, said Swedish Prosecution Authority spokeswoman Karin Rosander, reacting to the ruling. She maintained the prosecution authority has the right to issue an arrest warrant.

Assange spent nine days in London's Wandsworth prison after his arrest last year. He was freed a week before Christmas on bail and has since been living at the country house of a wealthy supporter in eastern England.

His arrest came shortly after WikiLeaks published thousands of secret U.S. diplomatic cables that included unflattering views of world leaders and candid assessments of security threats.

Assange says the allegations against him are politically motivated and has fought a complex and expensive legal battle to avoid being sent back to Sweden.

In 2010, WikiLeaks posted 391,832 secret papers on the Iraq war and 77,000 classified Pentagon documents on the Afghan conflict. It has also made available about 250,000 individual cables, daily traffic between the State Department and more than 270 American diplomatic outposts around the world.