Postcodes in the UK

I’ve noticed that a lot of visitors are reaching my site by searching for information on UK postcodes. So I might as well say something about them, and link to some sites I find useful.

The system of postcodes in the UK is (almost?) unique as a postcode pinpoints a small number of addresses – usually a street, or part of a street (for example the odd numbers). Properties receiving a lot of mail will have their own postcode. So in theory, your letter will get through if you write just the postcode and house number, although this may make life difficult for the postman who will have to remember which street it is for.

Postcodes were introduced between 1959 and 1974. Before then, mail was addressed using a postal town and county name. The latter ensured addresses were fairly unambiguous, although there are still some instances of multiple towns in a county having the same name. Postcode areas are determined by distance from sorting offices and do not follow county boundaries at all – in fact, they also cross the boundaries between England, Wales and Scotland.

The format of a postcode is X[X]n  dXX, where X is a letter, n is a number 0–99 and d is a single digit 0–9. The code may begin with one or two letters. Some places (parts of London) use the format X[X]dX  dXX. Using letters of the alphabet in place of digits increases the number of postcodes available – an advantage over the zip codes used in many countries.

Postal areas

The first one or two letters represents the postal area. It is usually an abbreviation for the largest town or city in the area. For example, “B” for Birmingham or “LE” for Leicester. Usually the first letter of the code is the initial letter of the town, and the second letter (if there is one) is another letter in the name of the town. There are some exceptions. Central London uses points of the compass: E, EC, SW, SE, W, WC, N, NW. “L” is actually the code for Liverpool. There are also a number of other codes that don’t quite match the names of the towns:

St Albans. Ignoring the “Saint”.
Dumfries. This probably stands for the name of the council area, Dumfries and Galloway, but that wasn’t created until 1975. The authorities must have had the name in mind long before then. Interestingly, “DF” is unused.
Blackpool. Actually stands for the nearby place, Fylde.
Hemel Hempstead. Does it just stand for Hempstead? Why not “HH”, which is unused?
Ilford. Why not “IL” or “IF”? Perhaps it’s to incorporate nearby Chigwell. Or perhaps they hit the same wrong typewriter key as for Dumfries.
Sutton. Could be blamed on a typo if “SN” wasn’t taken by Swindon. Maybe they decided to go for an adjacent code, although “SU” is untaken.
Salisbury. Perhaps “Salisbury Plain”?
Berwick-Upon-Tweed. Or “Tweedside”.
Middlesborough. Or “Teeside”.

Wikipedia has the full list of postal areas.

The remainder of the postcode

After the initial letter(s) comes a number representing the postal district. There can be up to 100 of these in a town as 0 is used. Often, 99 (and other high numbers) is used as the postcode for PO boxes.

After the postal district there is a space, which must be included for a correctly-formatted postcode. After the space are three characters which together represent the street, part of street, property or business.

The main post office in the town often has a postcode of the format XX1 1AA. One oddity is the postcode for Girobank, which was formerly part of the Post Office but is now owned by a commercial bank. This postcode is GIR 0AA – the equivalent of a personalised car number plate. It would be nice if the bank was located in Glasgow, but it isn’t.

There is lots more detail about postcodes at Wikipedia.

Finding a postcode or address

Royal Mail maintain a big database mapping postcodes to addresses. This is sold as a commercial product to companies, who use is as a quick way of entering addresses. If you’ve ever been asked for your house number and postcode, this is the reason.

There are several sites allowing the public to look up the postcode for an address or vice versa. They normally place a limit on the number of searches a user can make in a single day – obviously they don’t want companies using the database for free instead of paying for it! Royal Mail offer their own interface allowing 12 searches per day. But I prefer the service offered by AFD Software. Their interface allows more intelligent searches for addresses, will add the county name, and provides extra information about properties or businesses it finds. AFD allow 8 searches per day, so there’s 20 in total already…

Unfortunately, the address database isn’t perfect. I know at least one address where the entry in the database gives a misformatted street name. And because so many people use this instead of entering the address as given by the customer, most letters arrive with the address formatted wrongly.

That’s my brief introduction to postcodes. If you have any questions, comments, etc. please, as always, leave a comment.

55 responses to “Postcodes in the UK”

Showing comments 41 to 55

  1. Chris Downer

    The reason for the county anomalies is simply the cost-effectiveness of delivering mail from the nearest sorting office – which may well be in the neighbouring county. Although the postcodes came much later, a lot of the postal address infrastructure dates from the time when the railway took a lot of the post. For example, lots of small post towns in Wales on the BONCATH, CRYMYCH, CLYNDERWEN line and also in parts of Devon and Cornwall such as UMBERLEIGH, BEAWORTHY – these haven’t had a railway for 50 years and there is no way they could be considered ‘towns’.

    The KW anomaly is definitely just that. An anomaly.

    By the way, the letters C I K M O V never appear in the second half of a postcode!

  2. John Andrew

    I am showing you this address as when looking up the Postal Code address, or using any Satnav, it takes you to another part of the village-Wadham Close.
    When a family member had a stroke recently the Parmedics and ambulance went to the wrong address-causing a potentially dangerous delay.
    This must be changed. The house has been here for several hundred years, Wadham Close is a new estate.
    Who do we contact?

  3. Jonathan Rawle

    This sounds like a problem with the Postcode Address File (PAF) maintained by Royal Mail. There is an online form where you can report issues:
    If this doesn’t get you anywhere, you could try writing detailing the problem. Once changed in the PAF, it could take a long time to filter through to satnavs and other services, but you’d hope the emergency services update their data fairly frequently.

  4. Louise amberton

    Hi just making aware that the ‘S’ postcode is not just relevant to Sheffield it’s in fact South Yorkshire, as you will see some parts include Rotherham and Barnsley not just Sheffield, also checked with Royal Mail and they have clarified this too!

  5. James Lewis

    Try doing Internet searches for tradesmen, services, accommodation with an SY postcode. It’s a nightmare! They can’t tell the difference between Shrewsbury and Aberystwyth, a mere 75 miles apart.

    Mid and North Wales needs re-postcoding, urgently. Denbighshire and Flintshire should be WM (Wrexham/Wrecsam), it’s the largest town in the area by far, and how many places in Wales start with LL? Also limit SY to Shropshire (Ludlow is fully 30 miles from Shrewsbury as it is). MY (Montgomery/Maldwyn) and AH (Aberystwyth) should take the Welsh SY areas with CN (Caernarfon) and HH (Harlech) covering Gwynedd. Note that these codes work in both English and Welsh, unlike SY and CH.

  6. Frazer

    In relation to the question what is the largest town in the uk without its own post code

    The answer is the town of West Bromwich near Birmingham in the West Midlands I found this on

  7. Fleur

    HP actually stands for Harpenden, not Hemel Hempstead.

  8. Jonathan Rawle

    Would that be Harpenden, AL5?

  9. Sunil

    Maybe it’s IG because IL was thought to be easily miswritten as “11” or “LL”?


    I think IG is Ilford and Goodmayes.

  11. MFPA

    IG stands for “Ilford and Gants Hill”, according to the trainer we had when I worked for Royal Mail.

    FY is “Borough of Fylde Coast”.

    TD is “Borough of Tweedsdale”.

    SP is “Salisbury Plain”.

  12. Robert

    I thought IG would be Ilford and Goodmayes?

  13. Chris Warlow

    Does anyone know where I can find the location of an old postcode that now seems defunct. I recently bought something in an auction with the postcode CF3 9YP on the back.
    CF3 obviously still exists but the 9YP is drawing a blank, are there any Circa 1974 postcode maps available on line?
    Any help advice would be appreciated.

  14. Jonathan Rawle

    This site claims it is a defunct large user postcode:
    However, I don’t believe “June 1999” as the date it was deleted, as this seems to be the date it gives for all defunct postcodes. This site lists many such defunct postcodes:
    It’s likely it was a postcode allocated to a single business, rather than one that referred to a whole street. There are no results in Google giving an address, so it’s unlikely to have existed in recent years. Does the nature of the item give any clues as to what the business may have been?

  15. Amanda Starke

    Be careful with postcodes! I live in Pendarves street TUCKINGMILL In area of Camborne in Cornwall. I have found another 2 Pendarves streets within a mile and a half. Pendarves street THE BEACON, and Pendarves street TROON. Even though I have the correct postcode on my correspondence, everything is going to Pendarves street at THE BEACON, which happens to be an empty property! The post office swear blind that the post man knows where to deliver, but???

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