What is the U.K. insurance number?

It is a tax on your wages deposited into the National Insurance Fund, used to pay for various government-sponsored services. Your National Insurance (N.I.) number is unique to you and will remain so for the rest of your life; nevertheless, it is not a means of identification. Instead, it comprises two letters, six digits, and a final letter after the first two letters.
Anyone working in the U.K. must obtain an N.I. Number. To get a national insurance number, you must be 16 or older and live in the U.K. or Northern Ireland. You may begin working without one, but you will need to apply for a national insurance number as soon as possible if you do not already have an N.I. Number and are employed or expect to be used. You must apply for one under the terms of the legislation. The U.K. government provides national Insurance numbers to keep track of your tax and benefit entitlements.