The justices inevitably tread on the rim of the nation's laws -- the "outer markers" as Justice Stephen Breyer put it -- and must craft a constitutionally credible ruling that will establish precedent, addressing guidelines for courts perhaps many decades.

CNN: STORY HIGHLIGHTS

But the next implication is that tighter integration of the eurozone countries would put Britain more clearly on the outer ring of a two-speed Europe - less integrated and showing every sign of wanting to stay there.

BBC: Britain pushes hard choices for Europe's hard core