distance by Postcode - Google API?

Hello I have a website but want the functionality such that models can register through a form and fill in their postcode. On the front end, people can search for the models entering their own postcode and how far in miles they wish for the models to be, after which they will all come up and be displayed. The site is currently being developed by an expert php/mysql coder although the distance by postcode search to bring up the models is a mystery - any ideas? You will be required to work with the coder to implement this. I am looking for UK postcodes although having a UK and USA one would be advantageous. What would be even better is something that integrates with Googles API so that this function can facilitate the whole world. Thanks Rakesh