A National Insurance number is a reference number used by government. The easiest place to find your National Insurance number is on official paperwork, such as your National Insurance card, payslips or letters from the Department for Work and Pensions or HM Revenue & Customs (HMRC). Students may be able to find it in their university registration details or application for student loan. If you still can't find it, you can use the HMRC enquiry service at www.gov.uk/lost-national-insurance-number or call the helpline on 0300 200 3502.
Please be aware HMRC won't tell you your National Insurance number over the phone, they'll post it to you.
Most people in the UK have a National Insurance number. If you do not have one, you will be asked to explain why you are unable to provide it. Local electoral registration staff may contact you to ask you for proof of identity.