What letters do NI numbers end with?

National Insurance (NI) numbers in the UK typically end with a letter, and the possible endings are A, B, C, D, E, F, G, H, J, K, L, M, N, P, R, S, T, U, V, W, X, Y, and Z. However, some letters are not used as endings, such as S, T, U, V, W, X, Y, and Z for certain circumstances. The inclusion of a letter helps to distinguish between different types of NI numbers.