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 21 to 40

  1. Adrian

    I think “Tweedside” (TD) might be more accurately given as Tweeddale (hence the abbreviation – I don’t think it’s just to be distinct from TS).

  2. Mike

    My wife was brought up in Sutton and suggests that the postcode SM probably refers to Sutton and Merton (the adjacent borough). Thanks for an interesting, and very useful site.

  3. David

    The “IG postcode is Ilford and the “Green” in Woodford Green.

  4. Darren

    Blackpool is on the Fylde coast. There is not a place called Fylde it is the name on the coast line.

  5. chris

    Yes, the Fylde is the coastal plain between the Irish sea and the M6 which has Blackpool on it.

  6. chris

    The Ramsbottom area (north of Bury,Lancs.) has the postcode BL0 . I wonder how many other postcodes start x(x)0 cos most start x(x)1

  7. becky

    i hope you can help. i live on a farm ie with fields
    how can a farm with a distinctive boundary, a disused railway, have 3 different postcodes associated to the land all be it 2 small pockets on the railway bounhdary and 1 on someones elses property. our farm and the other have been owned privately for generations
    the postcode we use relates to the location of the farm house and yard.
    i look forward to your comments. please feel frre to email me direct.

  8. Keith

    Found your site while looking for some postcode info.
    One minor thing is that house number and postcode is not not a unique combination. Fair few duplicates in Glasgow I think, although the one that caused us many problems about 25 years ago with an address search system was a Bristol postcode of BS5 9NW, on which there were 8 ‘streets’ sharing the same postcode (possibly actually blocks of flats, but resulted in a house number and postcode coming back with 8 possibilities).

  9. Jonathan

    I tried BS5 9NW in the AFD Postcode Search. There are seven blocks of flats at this postcode, all located in Victoria Avenue. In this case, the name of the block, for example Adryan Court, is the equivalent of a house name, which takes the place of a house number. So Flat 1 Adryan Court, BS5 9NW is a unique address. If the blocks just had numbers, it would be Flat 1, 1, BS5 9NW. The street name, Victoria Avenue, is needed in neither case.

    What I omitted from my original description was that in the case of buildings that contain several flats with their own internal numbering, both the flat number and the building number/name need to be quoted. Many forms actually have a separate space for a flat number.

    Can you find any examples where a postcode refers to more than one street?

  10. Ben Adams

    Found this site whilst researching into the old Girobank. My feeling is that the postcode GIR 0AA as it was nice and easy to remember.

    Has anyone ever heard of their postcode being amended or completely altered within its own area? My aunts was changed from CW1 1LE to 5LE sometime in the 1990s, although I cannot see where the old code was moved to.

  11. Chris

    I lived in Salford Quays, initially under a M5 postcode. This was changed to M50 in the early 2000’s…

    Does anyone know which postcode covers the largest geographic area in England and also the UK please?

  12. Leanne

    Hi Jonathan,

    The SM I believe stands for Sutton and Merton which is the London Borough of.

    Hope this helps.

  13. Des

    Nearly four years ago(!), Martin Tobutt said:

    “Does anyone know what the largest UK town is without its own postcode? I see Windsor wants its own but I suppose it has something to do with sorting depots (or had in the past).”

    I presume you mean postcode *area*, Martin, since Windsor already has its own postcode *district* (SL4).

    Quite a few large towns don’t have their own postcode areas – Cheltenham uses GL50-4, Wrexham uses LL11-14, Rotherham uses S60-3/5/6, Barnsley uses S70-5, Grimsby uses DN31-4/6/7/41, Burnley uses BB10-12, Scarborough uses YO11-13 and Hartlepool uses TS24-7, while in Scotland Ayr uses KA6-8 and Stirling uses FK7-9.

    In the cases of Cheltenham, Rotherham, Barnsley and Grimsby, though, some sort of an effort has been made to distinguish their postcode districts by leaving out ones immediately beforehand. Hence, there is no GL21-49, S50-9, S67-9 or DN23-30.

    And – while not quite the same topic – most of the islands and island groups that *are* part of the UK don’t have their own postcode areas, either. The Isle of Wight uses PO30-41 (though, again, some effort at distinguishment has been made by leaving out PO23-9), Anglesey uses LL58-78, and the Isles of Scilly use TR21-5.

  14. wan

    i would like to ask, how the postcode UK boundary are determine? is it based on river or road? is there any algorithm to generate this boundary?

  15. Jonathan

    I think the boundaries were simply drawn around each major town to include areas most conveniently served by a particular office. They don’t necessarily follow geographical features (although this does of course have an influence). In some cases they roughly resemble county boundaries, but in many areas they don’t. Some postal districts even cross the border between Wales and England.

    The Ordnance Survey have a data file you can download under the Government’s open data policy, which contains details of every postcode in the country:

  16. Alan

    Your last comment aboout cross border postcodes raises interesting if somewhat silly issues re Wales and England e.g Aberystwyth has a Shrewsbury postcode ( 75 miles away) – also lots of Welsh border towns are linked to a large English town – eg Weshpool is linked to Shrewsbury (Welshpool is quite small abt 10000 people but a proper town nevertheless.

    It does not seem logical to have cross country codes. I believe the same issues affect England and Scotland border areas much to the annoyance of the residents.

  17. Jonathan

    Alan: I bet those residents are “annoyed” until you suggest that if they are in a different country they should be paying international postage rates. Then their views on a unified postal system might be slightly different.

  18. MikeW

    On cross-border postcodes…

    While nowadays, we tend to think of postcodes as belonging to a location (or vice-versa), the *original* purpose was for routing mail. Therefore, they don’t show where a property *is* but instead tell Royal Mail how to route mail towards that property.

    The first group of characters is used at the dispatch end – to indicate which delivery office the letter should be forwarded to.

    The second group of characters is then used at the receiving office – essentially to indicate which postman gets to deliver the letter.

    So if some Acottish properties get mail from an English sorting office, it gets an English postcode, and vice-versa.

    Aberystwyth is a bit extreme though!

  19. John BS

    I have two major frustations about hte English Post Code system.

    a) It has managed to totally destroy the coherence of Counties – often towns or Villages are given the address of a neighbouring because nearest postal centre happens to be in the next county. (West Sussex has no postcode at all relating to any town in the county – they all relate to towns in Hampshire, Surrey, Kent – apart from BN which is Brighton in East Sussex.

    b) Unlike most ISO format postcodes where the first couple of digits give a good indication to the area of the country (or in France’s case the department number) – the one or two letters used in England are often meaningless in determining which county (the main geographical; reference point for most people) a rough idea of where in the country it may be without a computer for areas one is not familiar with.

  20. Ally Gunn

    Have a look at the nonsense that is the KW postcode in the far north of Scotland. The KW stands for Kirkwall in Orkney yet it is only KW15!
    KW1 is in Wick. The first 14 KWs are on the mainland. Why was the area ever allocated a Kirkwall lettering? Why not WK? This is available. Another strange feature of this mess is that for some bizzare reason that nobody can work out, there is no KW4. Weird!

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