I respectfully disagree. WFB was a rara avis. It was not an English accent he had. It was his accent. He was a performer, no doubt. His accent was part of his performance. Buckley was the Ann Coulter of his time mutatis mutandis (although far more consequential).Naaah... Coulter and WFB as close to polar opposites as you can get. Anne is an entertainer, she says a lot of stuff but she really doesn't believe much of it(look into her personal life if you don't believe me). WFB was all about being a public intellectual and the "alpha male" of his particular jet set. That's why he did all the cruise stuff. That's also why he quietly fired anybody at the NR that might outshine him too.
Buckley spoke with “Locust Valley Lockjaw” which was the common accent of the Anglo and Dutch elite in the northeast (think FDR, Thurston Howell). You really don’t hear it much anymore.