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)
A side effect of the Social Security program in the United States has been the near-universal adoption of the program's identification number, the Social Security number, as the "de facto" U.S. national identification number. The social security number, or SSN, is issued pursuant to section 205(c)(2) of the Social Security Act, codified as . The government originally stated that the SSN would not be a means of identification, but currently a multitude of U.S. entities use the Social Security number as a personal identifier. These include government agencies such as the Internal Revenue Service, the military as well as private agencies such as banks, colleges and universities, health insurance companies, and employers.