Most UK residents will automatically be assigned a personal national insurance number around the time that they turn sixteen. A national insurance number is a personal identification number assigned to you by HM Revenue and Customs, and you need it so that the HMRC can keep correct track of how much tax and national insurance you have paid throughout your working life. You also need the number when applying for benefits, when in employment, or if you are a student and are applying for a student loan. There is a National Insurance Contact Number 0300 200 3500 that you can call if you have any queries to ask the HMRC specifically about things to do with national insurance.
Contacting the National Insurance phone number
If you are looking for a National Insurance Contact Number to call, there is, helpfully enough, a dedicated NI Contact Number 0300 200 3500 This number you can call, so you don’t have to go through a general customer enquiry 
line to have your queries answered. You may need to call the National Insurance Phone Number for a variety of reasons, although usually you will call the NI Contact Number if you need to apply for a national insurance number if you never received one, or if you have lost your national insurance number or card and want to ring the NI Phone Number to ask for a replacement card or a number reminder.
The National Insurance telephone number to call is 0300 200 3500, The people that will receive your call on the above telephone number will be happy to help in any and all matters regarding national insurance, whether you are just simply looking for more information about national insurance, or whether you need to apply for a national insurance number or a replacement national insurance card.
National Insurance contact number opening hours
The National Insurance contact number is open to take your enquiries between 8.30am and 5.00pm, Monday to Friday. It is to be expected that the line will be closed on public holidays and is also closed at the weekend. This is largely in line with other helplines currently in use by the UK Government and HMRC as a whole.
Other ways to contact National Insurance
If you feel the need to write to the National Insurance department, you will need to write to the central HMRC address. This is only really suggested for formal complaints, and for circumstances in which you have been asked for further documentation by the UK Government:
Please be aware that queries and complaints sent via post are likely to take longer to be dealt with. This is why we recommend calling the National Insurance contact number if you have any kind of problems.