Glossary
National Insurance number — explained for Turkish readers
The personal reference number used by HMRC and DWP to record a person's National Insurance contributions, tax and benefits. It is not an identity number.
A National Insurance number is a lifelong reference in the form of two letters, six digits and a letter, issued by the Department for Work and Pensions to anyone who works or claims benefits in the UK. Employers use it to report your contributions, HMRC to match your tax, and the DWP to calculate your State Pension. New arrivals apply for one once they have the right to work.
The Turkish reader may be tempted to treat it as the counterpart of the T.C. kimlik numarası, and that is a mistake. The NI number carries no identity function and is not accepted as proof of who you are; the UK has no national identity number. Its true counterpart is the SGK sicil numarası, and it is the number that matters when SGK asks for your UK contribution record for yurtdışı borçlanması.
NI records requested from HMRC are translated for that purpose; see SGK: buying back your years abroad.