LONDON — British authorities Tuesday blocked a longstanding demand for the extradition of Gary McKinnon, a computer hacker wanted in the United States to face charges of intruding into Pentagon computer networks in a case that has become a touchstone of the delicate jurisdictional balance between the two countries since the attacks of Sept. 11, 2001.

McKinnon, 46, who has been facing the accusations for a decade, suffers from Asperger’s syndrome and is prone to depression, British officials said.