National Insurance Number Information For Employers
All employees have an obligation to tell you their NI number when you ask for it. If they do not already have a number, they must, by law, apply for one as soon as they start work.
If the employee cannot remember their number, see if it is on any official
papers you may have for them e.g., form P45
or a married woman's certificate of election (CA 4139/ CF 383).
If you are still unable to find their number, keep a record of their full name, date of birth, sex and address. If you have to send form P46 to the Tax Office the Tax Office will automatically trace the employee's NI number and notify you on form CA6856.
If you do not have to send form P46 to the Tax Office you can either use the NI number tracing service or ask the employee to contact their local Social Security office (this link will take you to another web site) or HM Revenue & Customs (NI Contributions) office to find out what it is.
NI Number Tracing Service
Send completed form CA6855 available from any Social Security (this link will take you to another web site) or Tax Office to the address shown on the form. HM Revenue & Customs will trace the employee's NI number for you and notify you on form CA6856.
If you need to trace more than one employee's NI number you should use form CA6860 available from any HM Revenue & Customs office.
Remember to note this number on your records, then pass the form to the employee for future reference.