Tunesmith, other things I have read posited that a "Transatlantic" accent existed among internationally posh people on both sides of the Atlantic, particularly in English-speaking expat communities in places like Paris and Cairo.
Cole Porter would be another good example of this Transatlantic/Mid-Atlantic dialect and culture.

There's an entertaining YouTube video on the Transatlantic/Mid-Atlantic dialect here:

https://www.youtube.com/watch?v=Gpv_IkO_ZBU

-Joe-