As far as I know he's not staying in the UK. He's staying in Ecuador. He just can't leave Ecuador (actually its embassy) because he's surrounded by the UK, both at land and air.
As people have pointed out below, this is a myth. An embassy is not sovereign. It is on British soil and under British law. The reason embassies are not raided is diplomatic politeness. If it is was someone the US/UK really cared about they would be whisked away in the blink of an eye.
According to Wikipedia: "[...] the premises of diplomatic missions remain under the jurisdiction of the host state while being afforded special privileges (such as immunity from most local laws) [...] and (as an adherent to the Vienna Convention) the host country may not enter the premises of the mission without permission of the represented country"
I'm not a lawyer so that's as far as I know :) Seems applicable to this situation.
But people suggest (as an alternative) that Assange could stand trial / answer questions in the UK, implying that it's Sweden he doesn't want to go to. Which doesn't make sense. Why would he stay in the UK while the appeals to the UK Supreme Court were going ahead?
