You go to your local social security office and ask nicely. They will want to interview you , mostly to establish that you are a UK citizen entitled to one , and to check that you need one. I don't knwo how long it takes for it to then arrive.
Actually, if you go to the Jobcentre Plus Office they will give you a telephone number you need to ring to book an appointment for a National Insurance Number interview. (Unfortunately I don't remember the phone number off the top of my head.) National Insurance Numbers will only be given to people who (a) Are actively seeking work and can prove they are, (b) Actually working and can provide payslips/letter from employer etc, or (c) have made a claim to a UK benefit that they will be entitled to. You also obviously need to prove your identity.
Come to think about it, if you have previously lived in the UK, did either of your parents ever claim Child Benefit for you in the UK? If they did, there may already be a National Insurance Number already allocated to you. If that is the case, you may not need a full interview and someone may be able to do a specialist trace on their system to see if there is already one for you. If Child Benefit was paid for you, it may be worth you explaining this to the person you speak to when you ring the number that the Jobcentre Plus person will give you.
If you have to have the full interview, it can take several weeks for your National Insurance Number to be allocated to you. But you should be told how long you have to wait for it at the interview.
I think it's a beautiful county. It's steeped in history. Lincoln was recorded in the Doomsday book, some of the Da Vinci Code was filmed at Lincoln Cathedral, the Pilgrim Fathers sailed from Boston to America, there's the Boston Stump, Gibraltar Point, The Lincolnshire Wolds, Grimsby, Cleethorpes, oh... and Skegness! Three British Superbike teams are based in Lincolnshire too. Most veg that is bought around the country (fresh/frozen/canned) is grown in the county. I could go on....
I was in a similar position. Phone & ask what is required. At the time (over 20 years ago), AFAIR I simply sent my birth certificate & passport and was issued with an NI number & card within a few weeks.
Technically, Grimsby and Cleethorpes have not been in Lincolnshire since Humberside was formed in the '70s. (Unless they changed it back again after I left :-)
If we ever have such a thing, they might just be able to.
But we most certainly don't have anything even remotely approaching one-shop-national-government, never mind once you start including local government.
BeanSmart website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.