The problem is that UK based pilots paid in HKG, taxed in HKG but living in, for example, Cyprus,Majorca or Thailand are going to be taxed by Gay Gordon at source. This for spending possibly half a day in the UK twice a month to pick up your Chinese registered aircraft.
So, someone who by any measure is a non resident, is licenced, paid and taxed in HKG is also going to be taxed by the UK tax authorities. If this isn't a crime - it effin well should be.
This doesn't cover everyone, there are many that really do live in the UK (goodness knows why) and so they may be genuinely resident.