actually there are both emloyer and employee National Insurance contributions plus PAYE tax will be deducted at source for all UK based Employee's and then you will have to sort out on an individual basis your tax situation/ Liability......................
Obviously you will be able to offset any Hong Kong tax from your UK liability and if you are not actually Resident in UK you will ba able to get a "Nil Tax" code. however, the onus is now on the individual to prove his resident staus and then reclaim any tax paid, whereas before the UK tax man used to have to chase after people....................
Nasty business.................................