I am an American educated in a private school run by old school posh Brits. Up until the 8th grade (when we got cable) I had a posh British accent that leaned into Mid-Atlantic.

In 1999 I went to London for a Y2K preparations project and I could not understand about half of the words those fucks said.

EDIT: I should go to a vocal coach and try to get my mid-atlantic accent back. I think it's a fun accent to have.