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All about postcodes: facts and trivia

I don't know about you but when I'm addressing a letter, making sure the postcode is written in clearly legible handwriting makes it feel official - like I'm stamping the letter with an old-fashioned wax seal of approval.


Photo by: zappowbang

When a postcode is used, I know that the letter has the best chance of safely reaching its intended recipient (no matter how messy the rest of my handwriting looks). But postcodes are now regularly used by more people than just your average postie. For example, millions of us use them every day to plan our journeys with GPS software. So postcodes are an important part of what it means to be a UK citizen. White Pages utilises postcode data from the Telephone Directory and the Electoral Roll, but have you ever wanted to know more about what those series of letters and numbers actually mean? This article will explain some key facts and trivia about postcodes in Britain.

How Postcodes Started

Postcodes were introduced in Norwich in 1959 and took 15 years to become widely recognised and used by the whole of Britain. In 1857, Sir Rowland Hill came up with the first imaginings of what a postcode should do - which is to aid postal workers in sorting and delivering mail quickly.

As well as inventing the postage stamp, Sir Rowland Hill devised a post coding system that divided London into districts that corresponded to the main points on a compass (e.g. N, E, S, W, NE etc…) He then asked senders to label their post with these letters to speed up their delivery. But as we know, this system didn't stick. NE, for example now stands for Newcastle under the new post coding system.

How Postcodes Work

Britain is one of seven post coding systems in the world that use an alphanumeric system and is considered very effective because alphanumeric codes allow a greater number of unique combinations to be used.

A postcode will start with the Initial of the largest nearby town or city in the area followed by another letter that also appears somewhere in the town name (e.g. LE is the start of the postcode for addresses in Leicester). The first two letters are referred to as the postcode area and there are 124 of these in Britain. The number that follows the first two letters of a postcode will refer to the district within that area. There are approximately 3,000 postcode districts in the UK.

So, the letter/number combination in the first half of a postcode will tell us which sorting office the post needs to be sent to.

The second half of a postcode will then start with a number. This number tells the local sorting office which sectors of the district the letter needs to be sent to, thereby narrowing down the target location even further. There are approximately 9,000 of these different sectors.

The final two letters of the postcode refer to your individual unit representing on average 15 addresses each. A postman at this point will rely on the rest of the address information to put the letter through the right letterbox.

Special Exceptions

Not all postcodes fit in this neat little coding system and there are many exceptions to the rules. St. Albans for example carries the Area code of AL, which isn't what you would initially expect. Similarly, Salisbury carries an SP area code where perhaps you would have expected to see either a SL or maybe a SY instead.

The second half of the postcode, which represents the combination for one of 1.8 million units, cannot contain the letters C I K M O V. This is to prevent ambiguity between letters and numbers in non-standard handwriting styles. However, there are still plenty of combinations to choose from; in fact, 27 million postcodes are currently in operation in Britain.