Mauritius has threatened to sue Britain over delays to the Chagos island "surrender" deal.Navin Ramgoolam, the Prime Minister of Mauritius, last week warned Jonathan Powell, the UK national security adviser, he was prepared to "take the legal route" unless the issue was "expeditiously resolved".The Mauritian Prime Minister travelled to London to discuss the deal after it became a key point at the UN General Assembly (UNGA) in New York last month…