National Insurance number
The National Insurance number is a number used in the United Kingdom in the administration of the National Insurance or social security system. It is also used for some purposes in the UK tax system. The number is described by the United Kingdom government as a "personal account number".
British National (Overseas)
British Nationals (Overseas) are subject to immigration controls and have neither the right of abode or the right to work in the United Kingdom. BN(O)s are required to pay a "health surcharge" to access National Health Service benefits when residing in the UK for longer than six months. They are also ineligible for the Registered Traveller service, which enables expedited clearance through British immigration, despite HKSAR passport holders being eligible.