Step :1 Visit the site below
Step :2 Enter postcode in the top search box.
Step :3 Press the Search button
Step :4 Scroll down the page until you view this.
Step :5 Locate the grid reference and note the first two letters i.e SP and thats your areas grid code.
Step :6 Then on the top of the page you will see all the grid code links, select yours and start searching.