If you do not already have a NI number you must apply for one as soon as you start work or you or your partner claims benefit. You must be over 16 years old and resident in Great Britain.
Providing you satisfy these conditions, you should telephone Jobcentre Plus on 0845 600 0643 to arrange to get one.
Lines are open 8.00 am to 6.00 pm Monday to Friday.
Visit the HMRC website for more information.