UK Postcode search on first 1 or 2 letters

[geoff2404]

I'm trying to set up a search facility on a site, where viewers enter the first part of their postcode. Most UK codes begin with 2 letters - no problem. But some have just the one - e.g. Sheffield codes are just S followed by one or two numbers. If the user enters "S#", then the search works fine, but "S" finds all the other codes e.g. Shrewsbury "SY". It's an Access database, searched from an ASP page created by FP2000. Any suggestions? (a quick trawl of the web suggests this is a common problem...)