And then what are you going to do?
One of the things to remember about casting people is this: Much of the time, there is a point at which your casting choices become somewhat arbitrary. I've cast or helped cast theatrical productions, and often you hit a point where neither Actor A nor Actor B are truly "better" than one-another. You have to make a choice, so you go with your instinct, and it's probably a bit arbitrary.
If the Doctor Who
team were to make an effort to find the best actors out there who are not white Englishmen, obviously they would have to pick one person, and at some point their choice may well be somewhat arbitrary. That's okay. The goals would be to find a great actor, and to break out of the mindset that one should see "white English male" as the "default" setting.