BRUSSELS (Reuters) - Brexit Britain is part of an “arc of instability” that has emerged around the European Union, the bloc’s chairman said on Monday, ranking London’s decision to leave the EU along with threats from Turkey, Russia, Libya and Syria. “An arc of instability has developed all around us,” European Council President Charles Michel, who chairs EU summits, said in an online address for the Bruegel think-tank. “In the west, Brexit. ... The result shook up the European Union. This choice of national sovereignty was felt as a failure of European construction,” Michel said. “The truth is, the British face a dilemma. What model of society do they want??” Britain left the EU, the world’s largest trading bloc, on Jan. 31 after 47 years of partnership to the huge regret of EU leaders who now insist that London accept the economic consequences of looser ties. The process of negotiating a new trade relationship and finding Britain’s new place in the world is proving complicated and has revealed divisions within political parties, society and the government itself. The EU and Britain both said on Monday that a post-Brexit deal was still some way off and differences persisted over putting in place their earlier divorce deal as they began a decisive week of talks in Brussels.