Some 16,867 voters in southeast England ushered in a season of European political tumult that in an extreme scenario could lead to Britain exiting the European Union, Greece quitting the euro or Catalonia seceding from Spain.

Victory by the anti-EU U.K. Independence Party in a British parliamentary contest was fueled by the same sense of economic injustice and antagonism toward the status quo that will unsettle Europe in coming months. It also gave a flavor of the potential fallout, as the value of the pound tumbled against most of its 16 major peers.

"The markets have a lot to worry about," Edmund Phelps, a Nobel Prize-winning economist at Columbia University in New York, said in an interview before the British vote. "It's possible that we could see a swing toward the extreme right, and one must wonder what ramifications this would have for the European Union and the euro area."