World leaders played an interactive nuclear war game designed to test their responses to a terrorist atomic "dirty bomb" attack that threatened the lives of hundreds of thousands of people. David Cameron joined Barack Obama, Angela Merkel and Xi Jinping and other world leaders to play a "nukes on the loose" war game to see how they would cope with a terrorist nuclear attack. The German chancellor grumbled at being asked to play games and take tests with the Prime Minister, US and Chinese presidents around a table with dozens of heads of state at a nuclear summit in The...