The domestic NIN is divided into two categories. One is business, and the other is personal. Both numbers will be 12 digits long with the first three digits being a unique identifier. As mentioned, the NIN is the telephone number, postal address (circumstances apply), Educational ID number, One Care Number, and likely used in other instances.
For businesses, the first number will be a 1 with two digits following ranging from 0-9. These two numbers will represent an industry code. The following 9 digits is randomly created to provide a unique number.
For people, the first number will always be 2-9 with the second number being a 0 or 1. The third digit will be 0-9, and the remaining numbers will be random. This unique setup is to not conflict with foreign NIN numbers.