What you need to do ASAP: Get an NI Number
Why and how to get one quickly without loss of income or unnecessary frustration
Links to information below:
What is a National Insurance (NI) number - UK?
Your UK National Insurance number is a unique personal number allocated to you that is used to identify you to HM Revenue & Customs and the Department of Work and Pensions.
It ensures the Government correctly records any contributions you are entitled to. Your National Insurance contributions go towards the UK social security and the state pension system.
Everyone who works in any capacity in the UK will need to register for an national insurance number.
When do I need to use my NI Number?
If you intend to work in the UK, you need to apply as possible. You will need to quote your NI number to your employer's accounts department for taxation purposes and contributions will be taken each time you are paid.
If you don't have a NI number, you will be required to contribute more than normal in NI payments so it's wise to get yours as soon after arriving in the UK as possible. Further to this you
will not be able to claim any of your overpaid taxes back or opt to get a NI rebate. It is therefore vital to obtain this number when you start working.
The Revenue and Customs Department (the HMRC) no longer accept 'temporary' National Insurance numbers. After applying you will receive your National Insurance Number and card in the post a while later and you should ensure your employer is aware of this number.
If you have employment:
It is easier to apply for a NI Number once you have secured employment however it is better to get it ASAP so that you pay less emergency tax. In order to apply for the number you will need documentation to do with employment (such as a contract or letter from your employer).
If you are not yet employed:
If you have not yet secured employment you can still apply however certain documents will be required (such as job rejection letters, letters from your recruitment agent etc). Unless you use a service (see Online services below) in which case they can assist you with this.
How do I get my National Insurance (NI) Number?Source: money.workgateways.com