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 Agency (Northern Ireland)
The Social Security Agency is a government agency in Northern Ireland. It is a department within the Department for Communities (DfC), dealing with social security.