Question : Driving Distance between Postcodes

Afternoon all.

I'm developing a tool to calculate approximate travel expenses based on distance traveled between my office location in the UK and any other postcode.

So far I've done ok by working out straight-line distances using latitude/longitude but this isn't accurate enough.

Basically what I'm after is a list of all UK postcodes (just the first bit though eg M24, BL1) and the driving distance from my location (M24).  Does anybody know where I could get this information or if there are any services I could use as API for my Excel spreadsheet?

Hope you can help.
Matt

Answer : Driving Distance between Postcodes

My Access Archon #193 uses a Google Map on an Access form to get the distance between zip codes.  Here is a link for it:
http://www.helenfeddema.com/Files/accarch193.zip
And here is a screen shot of the form: