National Insurance number
The National Insurance number is used as a reference number in the Pay As You Earn system, and also by the self-employed. It is also used in applications for Individual Savings Accounts (ISAs), to check that an individual has opened only one ISA in a tax year.
Social Security (United States)
The analogy to insurance, however, is limited by the fact that paying FICA taxes creates no legal right to benefits and by the extent to which Social Security is, in fact, funded by FICA taxes. During 2011 and 2012, for example, FICA tax revenue was insufficient to maintain Social Security's solvency without transfers from general revenues. These transfers added to the general budget deficit like general program spending.