Taxpayers who have lost or forgotten their national insurance number should first try and locate the number on paperwork such as their tax return, payslip or P60. Taxpayers with access to their personal tax account can also login to view or print a letter with their national insurance number.

If the national insurance number cannot be located, a request can be submitted in writing to HMRC using form CA5403. The form has recently been updated. HMRC will not disclose the number over the telephone, and will instead send the details to the applicant by post. The details should arrive within 15 days.

Teenagers should automatically be sent a letter just before their 16th birthday detailing their national insurance number. These letters should be kept in a safe place. The old plastic national insurance cards that some of our readers may remember are no longer available.

The national insurance number helpline, can help those aged between 16 and 20 who have not received a letter with details of their national insurance number as well as other new applicants.

An individual must have the right to work or study in the UK in order to apply for a national insurance number.