It’s not just the accents. Often, it seems as if the reason that veteran thespians from the British Isles have been placed on earth is to get down with their bad selves. They bring a twinkle, a relish, a lordly theatrical swing to the cultivation of villainy that mirrors, in its very style, what’s so inviting about evil. Currently, there are two performances that embody that suavely relaxed drawing-room malevolence I can never get enough of. In Layer Cake, Michael Gambon, a great rogue of an actor, plays a silky London gangster who sits around his 18th-century study giving homicidal threats the finesse of poetry. With his mellifluous cocked-eyebrow joy, and a tan so deep it’s almost satanic, Gambon manages to steal scenes in a movie where every scene already amounts to a case of grand larceny. And in Star Wars: Episode III — Revenge of the Sith, Ian McDiarmid, as Supreme Chancellor Palpatine, chews on his lines with a plummy treachery that makes the dark side of the Force sound so seductive, I was genuinely sorry Hayden Christensen’s worrywart Anakin Skywalker couldn’t have had a bit more fun succumbing to it.