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".
Tax policy
National Insurance in the United Kingdom and Social Security in the United States are forms of social welfare funded outside their national income tax systems, paid for through worker contributions, something labeled a stealth tax by critics.