RegEx for matching UK Postcodes

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 in

Answer 1

What i have found in nearly all the variations and the regex from the bulk transfer pdf and what is on wikipedia site is this, specifically for the wikipedia regex is, there needs to be a ^ after the first |(vertical bar). I figured this out by testing for AA9A 9AA, because otherwise the format check for A9A 9AA will validate it. For Example checking for EC1D 1BB which should be invalid comes back valid because C1D 1BB is a valid format.

Here is what I've come up with for a good regex:

^([G][I][R] 0[A]{2})|^((([A-Z-[QVX]][0-9]{1,2})|([A-Z-[QVX]][A-HK-Y][0-9]{1,2})|([A-Z-[QVX]][0-9][ABCDEFGHJKPSTUW])|([A-Z-[QVX]][A-HK-Y][0-9][ABEHMNPRVWXY])) [0-9][A-Z-[CIKMOV]]{2})$

Answer 2

I wanted a simple regex, where it's fine to allow too much, but not to deny a valid postcode. I went with this (the input is a stripped/trimmed string):

/^([a-z0-9]\s*){5,8}$/i

This allows the shortest possible postcodes like "L1 8JQ" as well as the longest ones like "OL14 5ET".

Because it allows up to 8 characters, it will also allow incorrect 8 character postcodes if there is no space: "OL145ETX". But again, this is a simplistic regex, for when that's good enough.

Answer 3

I've been looking for a UK postcode regex for the last day or so and stumbled on this thread. I worked my way through most of the suggestions above and none of them worked for me so I came up with my own regex which, as far as I know, captures all valid UK postcodes as of Jan '13 (according to the latest literature from the Royal Mail).

The regex and some simple postcode checking PHP code is posted below. NOTE:- It allows for lower or uppercase postcodes and the GIR 0AA anomaly but to deal with the, more than likely, presence of a space in the middle of an entered postcode it also makes use of a simple str_replace to remove the space before testing against the regex. Any discrepancies beyond that and the Royal Mail themselves don't even mention them in their literature (see http://www.royalmail.com/sites/default/files/docs/pdf/programmers_guide_edition_7_v5.pdf and start reading from page 17)!

Note: In the Royal Mail's own literature (link above) there is a slight ambiguity surrounding the 3rd and 4th positions and the exceptions in place if these characters are letters. I contacted Royal Mail directly to clear it up and in their own words "A letter in the 4th position of the Outward Code with the format AANA NAA has no exceptions and the 3rd position exceptions apply only to the last letter of the Outward Code with the format ANA NAA." Straight from the horse's mouth!

<?php

    $postcoderegex = '/^([g][i][r][0][a][a])$|^((([a-pr-uwyz]{1}([0]|[1-9]\d?))|([a-pr-uwyz]{1}[a-hk-y]{1}([0]|[1-9]\d?))|([a-pr-uwyz]{1}[1-9][a-hjkps-uw]{1})|([a-pr-uwyz]{1}[a-hk-y]{1}[1-9][a-z]{1}))(\d[abd-hjlnp-uw-z]{2})?)$/i';

    $postcode2check = str_replace(' ','',$postcode2check);

    if (preg_match($postcoderegex, $postcode2check)) {

        echo "$postcode2check is a valid postcode<br>";

    } else {

        echo "$postcode2check is not a valid postcode<br>";

    }

?>

I hope it helps anyone else who comes across this thread looking for a solution.

Answer 4

To add to this list a more practical regex that I use that allows the user to enter an empty string is:

^$|^(([gG][iI][rR] {0,}0[aA]{2})|((([a-pr-uwyzA-PR-UWYZ][a-hk-yA-HK-Y]?[0-9][0-9]?)|(([a-pr-uwyzA-PR-UWYZ][0-9][a-hjkstuwA-HJKSTUW])|([a-pr-uwyzA-PR-UWYZ][a-hk-yA-HK-Y][0-9][abehmnprv-yABEHMNPRV-Y]))) {0,1}[0-9][abd-hjlnp-uw-zABD-HJLNP-UW-Z]{2}))$

This regex allows capital and lower case letters with an optional space in between

From a software developers point of view this regex is useful for software where an address may be optional. For example if a user did not want to supply their address details

Answer 5

I have the regex for UK Postcode validation.

This is working for all type of Postcode either inner or outer

^((([A-PR-UWYZ][0-9])|([A-PR-UWYZ][0-9][0-9])|([A-PR-UWYZ][A-HK-Y][0-9])|([A-PR-UWYZ][A-HK-Y][0-9][0-9])|([A-PR-UWYZ][0-9][A-HJKSTUW])|([A-PR-UWYZ][A-HK-Y][0-9][ABEHMNPRVWXY]))) || ^((GIR)[ ]?(0AA))$|^(([A-PR-UWYZ][0-9])[ ]?([0-9][ABD-HJLNPQ-UW-Z]{0,2}))$|^(([A-PR-UWYZ][0-9][0-9])[ ]?([0-9][ABD-HJLNPQ-UW-Z]{0,2}))$|^(([A-PR-UWYZ][A-HK-Y0-9][0-9])[ ]?([0-9][ABD-HJLNPQ-UW-Z]{0,2}))$|^(([A-PR-UWYZ][A-HK-Y0-9][0-9][0-9])[ ]?([0-9][ABD-HJLNPQ-UW-Z]{0,2}))$|^(([A-PR-UWYZ][0-9][A-HJKS-UW0-9])[ ]?([0-9][ABD-HJLNPQ-UW-Z]{0,2}))$|^(([A-PR-UWYZ][A-HK-Y0-9][0-9][ABEHMNPRVWXY0-9])[ ]?([0-9][ABD-HJLNPQ-UW-Z]{0,2}))$

This is working for all type of format.

Example:

AB10-------------------->ONLY OUTER POSTCODE

A1 1AA------------------>COMBINATION OF (OUTER AND INNER) POSTCODE

WC2A-------------------->OUTER

Answer 6

I'd recommend taking a look at the UK Government Data Standard for postcodes [link now dead; archive of XML, see Wikipedia for discussion]. There is a brief description about the data and the attached xml schema provides a regular expression. It may not be exactly what you want but would be a good starting point. The RegEx differs from the XML slightly, as a P character in third position in format A9A 9AA is allowed by the definition given.

The RegEx supplied by the UK Government was:

([Gg][Ii][Rr] 0[Aa]{2})|((([A-Za-z][0-9]{1,2})|(([A-Za-z][A-Ha-hJ-Yj-y][0-9]{1,2})|(([A-Za-z][0-9][A-Za-z])|([A-Za-z][A-Ha-hJ-Yj-y][0-9][A-Za-z]?))))\s?[0-9][A-Za-z]{2})

As pointed out on the Wikipedia discussion, this will allow some non-real postcodes (e.g. those starting AA, ZY) and they do provide a more rigorous test that you could try.