UK Postcode Regex (Comprehensive)

Question

I'm after a regex that will validate a full complex UK postcode only within an input string. All of the uncommon postcode forms must be covered as well as the usual. For instance:

Matches

• CW3 9SS
• SE5 0EG
• SE50EG
• se5 0eg
• WC2H 7LT

No Match

• aWC2H 7LT
• WC2H 7LTa
• WC2H

Are there any official or even semi-official regexes in use for this kind of thing? Any other advice as to formatting and storing these in a database?

Answer 1

According to this Wikipedia table

This pattern cover all the cases

(?:[A-Za-z]\d ?\d[A-Za-z]{2})|(?:[A-Za-z][A-Za-z\d]\d ?\d[A-Za-z]{2})|(?:[A-Za-z]{2}\d{2} ?\d[A-Za-z]{2})|(?:[A-Za-z]\d[A-Za-z] ?\d[A-Za-z]{2})|(?:[A-Za-z]{2}\d[A-Za-z] ?\d[A-Za-z]{2})

When using it on Android\Java use \\d

Answer 2

Have a look at the python code on this page:

http://www.brunningonline.net/simon/blog/archives/001292.html

I've got some postcode parsing to do. The requirement is pretty simple; I have to parse a postcode into an outcode and (optional) incode. The good new is that I don't have to perform any validation - I just have to chop up what I've been provided with in a vaguely intelligent manner. I can't assume much about my import in terms of formatting, i.e. case and embedded spaces. But this isn't the bad news; the bad news is that I have to do it all in RPG. :-(

Nevertheless, I threw a little Python function together to clarify my thinking.

I've used it to process postcodes for me.

Answer 3

Here's a regex based on the format specified in the documents which are linked to marcj's answer:

/^[A-Z]{1,2}[0-9][0-9A-Z]? ?[0-9][A-Z]{2}$/

The only difference between that and the specs is that the last 2 characters cannot be in [CIKMOV] according to the specs.

Edit: Here's another version which does test for the trailing character limitations.

/^[A-Z]{1,2}[0-9][0-9A-Z]? ?[0-9][A-BD-HJLNP-UW-Z]{2}$/

Answer 4

Some of the regexs above are a little restrictive. Note the genuine postcode: "W1K 7AA" would fail given the rule "Position 3 - AEHMNPRTVXY only used" above as "K" would be disallowed.

the regex:

^(GIR 0AA|[A-PR-UWYZ]([0-9]{1,2}|([A-HK-Y][0-9]|[A-HK-Y][0-9]([0-9]|[ABEHMNPRV-Y]))|[0-9][A-HJKPS-UW])[0-9][ABD-HJLNP-UW-Z]{2})$

Seems a little more accurate, see the Wikipedia article entitled 'Postcodes in the United Kingdom'.

Note that this regex requires uppercase only characters.

The bigger question is whether you are restricting user input to allow only postcodes that actually exist or whether you are simply trying to stop users entering complete rubbish into the form fields. Correctly matching every possible postcode, and future proofing it, is a harder puzzle, and probably not worth it unless you are HMRC.

Answer 5

Basic rules:

^[A-Z]{1,2}[0-9R][0-9A-Z]? [0-9][ABD-HJLNP-UW-Z]{2}$

Postal codes in the U.K. (or postcodes, as they’re called) are composed of five to seven alphanumeric characters separated by a space. The rules covering which characters can appear at particular positions are rather complicated and fraught with exceptions. The regular expression just shown therefore sticks to the basic rules.

Complete rules:

If you need a regex that ticks all the boxes for the postcode rules at the expense of readability, here you go:

^(?:(?:[A-PR-UWYZ][0-9]{1,2}|[A-PR-UWYZ][A-HK-Y][0-9]{1,2}|[A-PR-UWYZ][0-9][A-HJKSTUW]|[A-PR-UWYZ][A-HK-Y][0-9][ABEHMNPRV-Y]) [0-9][ABD-HJLNP-UW-Z]{2}|GIR 0AA)$

Source: https://www.safaribooksonline.com/library/view/regular-expressions-cookbook/9781449327453/ch04s16.html

Tested against our customers database and seems perfectly accurate.

Answer 6

We were given a spec:

UK postcodes must be in one of the following forms (with one exception, see below): 
    § A9 9AA 
    § A99 9AA
    § AA9 9AA
    § AA99 9AA
    § A9A 9AA
    § AA9A 9AA
where A represents an alphabetic character and 9 represents a numeric character.
Additional rules apply to alphabetic characters, as follows:
    § The character in position 1 may not be Q, V or X
    § The character in position 2 may not be I, J or Z
    § The character in position 3 may not be I, L, M, N, O, P, Q, R, V, X, Y or Z
    § The character in position 4 may not be C, D, F, G, I, J, K, L, O, Q, S, T, U or Z
    § The characters in the rightmost two positions may not be C, I, K, M, O or V
The one exception that does not follow these general rules is the postcode "GIR 0AA", which is a special valid postcode.

We came up with this:

/^([A-PR-UWYZ][A-HK-Y0-9](?:[A-HJKS-UW0-9][ABEHMNPRV-Y0-9]?)?\s*[0-9][ABD-HJLNP-UW-Z]{2}|GIR\s*0AA)$/i

But note - this allows any number of spaces in between groups.