LONDON (Reuters) - British Prime Minister David Cameron conceded on Sunday that Scotland had what it takes to be an independent nation, but said it currently enjoyed "the best of both worlds", imploring it not to break the United Kingdom apart. Stepping up his government's campaign to hold Britain together ahead of an independence referendum expected next year, Cameron urged Scotland not to sever a union with England that dates back 306 years. "Put simply: Britain works. Britain works well. Why break it?" he wrote in an article published in Scottish newspapers. ...