Fareaster, you either earn your money through the UK or HK system - not both. If it is through the UK system and you are UK resident, HK taxation does not even come into it.
If on the other hand you earn your money through the HK system whilst being UK resident, you pay HK tax and declare this as foreign income on your UK tax return - paying retrospectively to begin with.
The Revenue are well within their rights to ask you to make a payment "on account" for future earnings, but you are equally within your rights to point out to the Revenue that you will already have paid the first X% to a country with whom they have a DTA.
Before you or anyone else make any important decisions on working for a foreign carrier, you might want to speak with a tax advisor.