Your National Insurance Number (NINO) is used as your unique reference number for the UK social security system throughout your life.
It helps HMRC make sure your tax and National Insurance (NI) contributions are recorded against your name. This is important because your entitlement to certain benefits, like the State Pension and Incapacity Benefit, depends on how much NI you’ve paid previously.
Everyone who works in the UK has to contribute to the social security system by paying NI, unless you have a special exemption. This applies even if you’re only working here temporarily. You can start work without a NINO, but must apply for one immediately.