“Hugh Laurie as tv’s House, whom I would never have taken as British had I not been so informed”
That’s not quite true. You can hear it when he yells, sings, and talks fast. But the rest of the time it’s uncanny.
One of the more remarkable hiding of accent was by the actress who portrayed Deanna Troi on Star Trek: TNG.
Her natural accent is very heavy British of some region and is glaringly different from her on-screen accent.