WikiLeaks' founder Julian Assange's possible final legal challenge to stop his extradition from Britain to the United States where he is wanted on criminal charges will be held at London's High Court in February, his supporters said on Tuesday. Assange, 52, is wanted by U.S. authorities on 18 counts, including one under a spying act, relating to WikiLeaks' release of vast troves of confidential U.S. military records and diplomatic cables which Washington said had put lives in danger.