A (possibly silly) question from an observer, are the Hong Kong staff employed in Hong Kong on local contracts? if so why would UK law be relevent? or, are they on UK contracts?
If this went against BA what would the implications be for, as an example, someone who is employed by BA who lives/works in France working at CDG as local managers? Could BA then say to that person you are now on a UK contract with the following xyz reductions in T&Cs? and if you don't like it you can blame the unions as they won a case to say that overseas employees should be treated as though they were in the UK?