Kathleen Turner has British theatergoers’ knickers in a twist. The actress, 45, appears stark naked in the new stage version of “The Graduate,” based on the 1967 movie that made a star of Dustin Hoffman. Turner plays Mrs. Robinson, who seduces recent college grad Benjamin Braddock, played onstage by Matthew Rhys. (Anne Bancroft played Mrs. Robinson in the film.) The theater production, which opened in London’s West End on Monday night, features Turner’s Robinson stepping out of the bathroom wearing only a towel — which she then drops to the floor. For the rest of the scene, Turner is starkers. “At the moment the towel came off, a kind of gasp — of surprise or delight or horror — went around the audience,” reported the Evening Standard. The applause was said to be riotous. In the movie, Mrs. Robinson only removed a stocking.