The founder of the WikiLeaks whistle-blowing website, accused of the sex attacks by two former volunteers, had argued that the European Arrest Warrant issued for him was invalid because it was made by prosecutors rather than a judge.
The Supreme Court, Britain's highest court, on Wednesday rejected his claim in a ruling made by a 5-2 majority of senior judges.
Lord Phillips, the president of the court, said 'judicial authority' could mean a prosecutor.
But lawyers for the maverick Australian, responsible for the publication of thousands of American diplomatic cables and sensitive military files, indicated they may try to have the case reopened.
They said it was decided on a point not raised in the hearing, and were given 14 days to lodge a claim.
