AFP - British Prime Minister David Cameron threatened to block a new European Union treaty designed to save the euro from the debt crisis if London's demands are not met. Cameron said Britain's huge financial sector and the single market would have to be protected if he were to sign up to a new EU-wide treaty aimed at resolving the crisis in the euro, which Britain does not use. His threat increases the likelihood that France and Germany, who proposed rewriting the treaty Monday, will end up pushing for an agreement between just the 17 nations who use the euro...