LONDON, **v 18 (Reuters) - A nuclear agreement between Iran and six major powers can be reached by a **v. 24 deadline, British Foreign Secretary Philip Hammond said on Tuesday, but Tehran needs to show more flexibility in negotiations. "I believe a deal can be done," Hammond said following a London meeting with U.S. Secretary of State John Kerry. "But we will **t do a bad deal. These negotiations are extremely tough and Iran needs to show more flexibility if we are to succeed. ...