It should also be noted that the postcodes, and also the full postal addresses, do not follow local government boundaries. The London postal district follows an area much smaller than the boundaries of the Greater London Authority and many areas in outer London have the more standard form of postcode. Some areas have their old county name, and not London, in the address - for example letters to the borough of Kingston-upon-Thames have Surrey in the address, not London, although attempts are being made to correct this. And confusing matters further some postcodes, such as KT4 for the Worcester Park area spread over county and even regional boundaries. These problems exist outside of London as well and there are many examples of people in rural villages having postal addresses that do not contain the village's name.
British Postcode Prefixes (including overseas posessions)