Actually, it's not a matter of government intervention as much as it is the failure of business practices that limit the job market.
If there was a viable market for investing in UK- or European-owned airlines with UK- or European-only employees to serve UK or Europe, whay have they not been certificated and why are they not thriving? Airplanes cost the same, regardless of where they are delivered. Hiring local labor should be advantageous to local businesses. Why did it take a 49% investment by Atlas (not to mention a lot of campaining and arm-twisting to even find a UK "partner") to start GSS? Why didn't John Porter and/or Eddie Foyle or some other UK group start GSS on their own several years ago?
I work for a US airline with several British, German, Australian, New Zealand, South African, and Canadian citizens. Jobs are available, though maybe not in the quantities some would like. Likewise, I know several Americans working for China Air, KAL, and a few other non-US airlines.
Finally, don't forget that Europe is NOT a single country, so the arguments regarding cabotage within "Europe" just don't wash, regardless of how advantageous it may make it for some.