Regular Expression to validate UK National Insurance Number

Question

I have the following regular expression which validates the British National Insurance Number

^([a-zA-Z]){2}( )?([0-9]){2}( )?([0-9]){2}( )?([0-9]){2}( )?([a-zA-Z]){1}?$ 

Accepted values are:

AB 12 34 56 A  AB123456A 

I want this values also to be accepted. can anyone please help me sort out this?

AB 123456 A  AB 123 456 A  AB 1 2345 6 A      AB   12   34   56 A    (multiple space anywhere) 

The RE should work even if there are extra or no spaces in the string. Is this possible to do in RE? Thank you in advance.

Answer 1

Actually, NIN doesn't allow D, F, I, Q, U or V for the first two letters and doesn't allow O for the second letter; on top of this, the prefix letters can not be BG, GB, NK, KN, TN, NT and ZZ. Also the suffix letter is either A, B, C or D, but may be represented by a space if unknown. - http://en.wikipedia.org/wiki/National_Insurance_number#Format

As such, a more valid check would be (I have only supplied a version with capital letters, can easily be altered for lower-case):

^(?!BG)(?!GB)(?!NK)(?!KN)(?!TN)(?!NT)(?!ZZ)(?:[A-CEGHJ-PR-TW-Z][A-CEGHJ-NPR-TW-Z])(?:\s*\d\s*){6}([A-D]|\s)$ 

Answer 2

Edit: Andrew Bauer modified my answer to add checks for allowed/disallowed characters that were unknown at the time I answered. You should up-vote his answer since it is more complete and apparently performs better validation.

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If you can't just remove all the whitespace first, this should work:

^\s*[a-zA-Z]{2}(?:\s*\d\s*){6}[a-zA-Z]?\s*$ 

Explanation:

^                 # beginning of string \s*               # optional leading whitespace [a-zA-Z]{2}       # match two letters (?:\s*\d\s*){6}   # six digits, with optional whitespace leading/trailing [a-zA-Z]?         # zero or one letter \s*               # optional trailing whitespace (just in case) $                 # end of string