User blog comment:SaganamiFan/Aidan Gillen/@comment-94.192.154.162-20130507020242/@comment-5014364-20130508013500

My...assumption, is that Aidan intentionally uses his natural Irish accent only when Baelish is particularly angered, which rarely happens. Case in point, in "What is Dead May Never Die" when Baelish is furious that for once, someone used HIM as a pawn in a deception (Tyrion) -- So what I inferred is that when he's in his normal calm, in control, smug, sleazy mode, he speaks with an adopted "refined King's Landing accent" (closer to a standard RP accent) but the idea is that the character shifts to his normal accent in rare moments of great anger, his natural accent from out in the Fingers in the Vale of Arryn, to emphasize by this "out of character moment" that he's really angry.

This is one of the things to ask the cast and crew.