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.

Leave a comment

By browsing this site, you agree to its use of cookies. More information. OK