UK latitude longitude radius calculation

Hi,

I have a database with UK postcodes and their latitude and longitude data.

What I want to do is have a search on my website and where a user can enter a postcode and select a radius like 5 miles. Then I want the search to only bring up companies from my database that are within this 5 miles radius.

Anyone got any idea how to calculate that?

 

http://www.phpro.org/tutorials/Geo-Targetting-With-PHP-And-MySQL.html

 

Thank you. Exactly what I needed.