Good question. If you are UK based but live elsewhere you will need to declare yourself 'non-resident'. You will then likely pay a percentage of UK tax based on your operating movements into and out of UK airports - the "formula" is yet to be clarified but if you worked on 1.5hrs per movement as a % of 84 duty hours you will be in the ballpark. It also seems that HK want a share if you spend more than 60 days there per year (
) Why they are entitled to this is anyone's guess... you will pay the HK taxman then use this as a tax credit.
Will you then pay other european tax? Probably! The UK HRMC is obliged (as I understand) it to inform other EU tax authorities if you declare yourself non resident.
As you will be employed by CX UK (i.e. a UK company) you will need to check the tax agreement between the UK and the country you are living in... just check the UK tax website.
This is a very fluid situation and is changing daily. Perhaps the old adage of planning for the worst and hoping for the best might be useful...
Someone else might be able to help you with the roster question.