What's in a postcode?

The answer is quite a lot. Most of us can remember our postcodes, but what exactly do the letters and numbers mean and why does St Teath confusingly have a postal address of Bodmin?

The Post Office introduced postcodes between 1959 and 1974 to enable mail to be sorted more efficiently, but they have since been used for many other purposes, including public services, some of which have been described as a 'postcode lottery'.

The postcode of The Square, St Teath, is PL30 3JT, which can be broken down as shown.

Postcode information for The Square, St Teath

When the code was devised, St Teath was allocated to Bodmin area PL30 as a post town. Postcodes are not coincident with Parish or Electoral Ward boundaries, so Delabole, in the same Parish, was allocated PL33. The Camelot Electoral Ward extends from Michaelstow through St Teath and Delabole to Tintagel.

Take a look at the map of PL30 below (Local postcode 'town' areas) and you will see that St Teath is in the most northerly part of the PL30 area which extends almost to St Austell. No wonder people have been known to look for St Teath in Bodmin. By contrast, Delabole was allocated a post town status, PL33, presumably because of its larger population. PL30 is one of the largest postcode areas in Cornwall.

Local postcode 'town' areas

It is the last two letters of the postcode which define the area of a group of houses in St Teath. The number of houses varies, but it is generally between 1 and 15 - very few houses have a unique postcode, and none in St Teath. Postcodes are copyright of the Post Office and a set of UK codes is very expensive; a complete edition and three quarterly updates costs £1,700 plus a licence fee, see here. Contrast this with the United States where the use of US zipcodes is free. However, given the address of a house, you can look up 15 UK postcodes/day free of charge on the Post Office website.

We cannot list all the St Teath postcodes here, but you can get a good idea of how they are distributed - see coded map of St Teath below.

All St Teath postcodes take the form PL30 3##, where the two ## letters are circled in white

It is the precise geographical location of these postcodes which proves so useful in the provision of services, both public and private. The Post Office data file referred to above contains a list of postcodes along with their latitudes and longitudes. Examples of usage include:

Widely available satellite navigation devices can provide accurate latitudes and longitudes to position a postcode and provide a way of duplicating data in the postcode file, see here.

Late in 2009 the government intimated that postcode data should be freely available to encourage digital innovation. However, Royal Mail, who owns tha database is resisting this because it is a valuable source of revenue. See www.ernestmarples.com for news of the latest developments.

Update 2011

Postcode data can now be downloaded free from this Ordnance Survey website.