I recently delved into working with UK Post Codes, including validation and searching. This is not my first contact with this area, and in the past it has always involved large SQL tables or by using third-party products.
This time, I was looking for something a bit more portable, like XML.
I was able to find freeware downloads of UK Post Codes including their longitude and latitude, which was easily imported into a SQL Server database.
I've created a class library called PostCodes.UK, which contains useful methods for validating post codes and determining which post codes fall within a given radial distance from a target post code. All of the search and validation routines utilise LINQ to XML to query the XDocument.
The class library relies on a PostCodes.xml file (supplied in the Test Harness project), which gets loaded as an XDocument. I've included a small WPF Test Harness application which illustrates how this library is used.
To run this solution you will need Visual Studio 2008 SP1. The source code is available here.
For those interested in this area, there is an informative government page on Postal Geography, which explains the structure of the UK post codes. You should be aware that UK post codes are always changing; however, if all you need is outward code resolution (e.g. PO6 ), chances are you can make do with public domain data.
Another site with useful information is: http://www.easypeasy.com/guides/article.php?article=64