You'd better hope that the rest of the World doesn't apply the same standard, or there might be so many highly qualified and experienced Brits returning home, that you might never, ever, find a job in the Aviation industry again!
An accent or origin from outside one country, is not indicative of the legal right to live and work in another country. People from all over the World, live in countries other than their country of birth for a variety of reasons and choices.
Would your selection be limited to Pilots only, or to all Airline personell and management as well?
Maybe your policy would start with Rod Eddington and Barbara Cassini, as these damn foreigners seem to be infiltrating every part of the British aviation industry?
I understand the concern of ANYONE looking at losing their livelihood or living, but think hard about what you are discussing here!