The chief executive of Swiss bank UBS has resigned over an alleged £1.5bn ($2.3bn) rogue-trading loss. \"Oswald Gruebel feels that it is his duty to assume responsibility for the recent unauthorised trading incident,\" Chairman Kaspar Villiger said in a statement. London-based trader Kweku Adoboli has been charged over the affair. UBS Europe chief Sergio P Ermotti would take over as interim chief executive, the bank announced.