The term "astronaut family" is often used to describe a family which is spread across the world.  Typically, the breadwinner of an immigrant family is the "astronaut" who travels frequently between the former and new countries of residence.  This type of family arrangement gathered momentum in the 1980s amongst Chinese immigrants in countries such as Australia, Canada and the US.

Before January 2018, dependants of UK points-based system ("PBS") visa holders could qualify for Indefinite Leave to Remain ("ILR") (i.e. permanent residence) in the UK regardless of their absences from the UK.  However, for PBS dependant visas granted after January 2018, the same rules on absences apply to the main visa holders and the dependants so that they will not qualify for ILR in the UK if their absences exceed 180 days in any 12-month periods.  Therefore, it was no longer advantageous for the breadwinner to apply as a dependant to avoid the 180-day rule.

The Home Office has confirmed that BN(O) holders and their dependants "should travel together to the UK as a family unit" under the new Hong Kong BN(O) visa.  It means that it is not possible for a family member to remain in HK (e.g. for employment or business ) whilst the rest of the family relocate to the UK.

If the HK BN(O) visa holders would like to qualify for ILR after 5 years of residence in the UK, then it is likely that they will become resident in the UK for tax purposes.  The tax year in the UK and HK are not quite aligned.  There is no Capital Gains Tax or Inheritance Tax in HK which are currently taxed at up to 28% and 40% respectively in the UK.  

Pre-immigration UK tax-planning advice should be sought and the advice should be implemented before the relocation takes place in order to minimise the chances  of receiving an unexpected skyrocketing tax bill from HMRC.