Hi Jan Muhl,
I can confirm that you are only allocated with one National Insurance number, and this will never change.
You can check what HMRC hold on your National Insurance contributions records, information on how to do this can be found here -
Check your National Insurance record
If there is no record of your previous employment on your National Insurance contributions records, you will need to provide HMRC with the further information –
Please write to -
Individual Caseworker
PT Operations North East England
HM Revenue & Customs
BX9 1AN
Please include the following information -
• all employer details which should include employers name and address, staff/payroll number (if known) and the tax year the earnings are missing from
• evidence of your earnings during the period for example pay slips, P45 or P60 certificates
• your personal details specifically your full name (with previous names, if applicable), date of birth, address, a contact number and your National Insurance number
• your signature
If you do not have any evidence, please provide as much information as you can.
Thank you.