Google Maps Questions

There is no data on precise co-ordinates of individual addresses, but
post codes are pretty accurate... average of 13 addresses per postcode
as far as I can remember.

A good place to go for co-ordinates is here:

http://www.samknows.com/toys/coords.php?output=xml&pc=se270nb,sw47ln,s118th,s101nu

You can list the postcodes seperated by commas as I've shown, and it
gives you a nice XML output of postcodes with their co-ordinates.