harrypic
Unfortunately you are wrong in your assumptions. They are not Non Doms. I believe they are considered as not ordinarily resident.
They pay tax in the UK on earnings whilst in the UK. As they spend a lot of time overseas for work these earnings are not taxed in the UK.
As long as their country of residence has a reciprocal agreement with the UK then a good proportion of their salary can be tax free,
I believe it is an old maritime arrangement. Again I believe the UK revenue has tried to repeal the rules but it is rumoured they have been thwarted by MEPs who use the same rules.
In short there can be a tax advantage in commuting from overseas.
That's why so many cabin crew work part time from overseas as the take home pay can be the same as full time and living in the UK.