Postcode Search Usability Fail

[RANT]
When searching online for goods in stock in nearby stores, I get really wound up by having to put in a full postcode. This is normally mildly annoying, in that I know my own full postcode, but there are some places for which I only know a partial postcode.

Example: I live in Kent, but work in Hampshire. The local Argos doesn't have stock of the printer ink I need, but it is listed, and is available for home delivery. PC World, Comet, Curries, Tescos, etc, no longer stock the ink.

I attempt to search the Basingstoke store. I enter "RG21", which I know is the town centre. It's rejected because it's not a full postcode, even though an area postcode should be sufficiently accurate in this instance. Grrrr!
[/RANT]