web service to calculate the distance between 2 UK postcodes

I need to calculate the distance between 2 UK postcodes... so needed webservices to test the same I tried below webservices but not able to figure out which function needs to be used.

I would appreciate if you know better/current web service to use.

http://www.SimplyLookupadmin.co.uk/WebService.asmx?WSDL
http://ws.cdyne.com/psaddress/addresslookup.asmx?wsdl
http://www.freewebservicesx.com/GetGoldPrice.asmx?WSDL 

thanks