In the television show Frasier, the protagonist's brother, Niles Crane, is a haughty, snobby, obsessive-compulsive psychiatrist who frequently obsesses about knowing the right people and climbing the social ladder. Unique to him is his accent, which serves to complement his upper-class persona.
People often call the stereotypical "upper-class" accent the Mid- or Trans-Atlantic accent, but this certainly doesn't describe the accent in question. While the Transatlantic accent includes clipping "r" sounds in words like "butter," Niles's accent is abounding in rhoticity (c.f. 0:09 in the video: "I'm afraid what the humidity will do to these loafers. Does calfskin pucker?"). Furthermore, he doesn't have the Transatlantic accent's characteristic sharp "t" in words like "getting" and "better" (c.f. 2:25 and 3:31, respectively, where he substitutes "d" for "tt".).
I was wondering what this accent is called, the regions it existed (or exists) in, and the story behind its apparent rarity/decline, as I've never heard it before.