I just found a useful file on Dan Huby’s website where he has compiled a list of all the neighbouring postal regions in the UK. This is useful if you want to build a postcode based search script, as you can match the actual searched for postcode as well as adjoining postcodes.
For example, from this file, the neighbouring postcodes of GU are:
GU,SL
GU,RG
GU,SO
GU,PO
GU,BN
GU,RH
GU,TW
GU,KT
Hey,
This sounds ideal for what I’ve been looking for, you wouldn’t by any chance have a copy of this still?
The website looks like it’s down