Type http://www.royalmail.com into your internet browser's window and hit Enter. Click on the "Small & Medium Business" button. In the "Tools" box on the right side of the page, click "Postcode Finder".
Enter the address of the business for which you wish to find the rateable value, and click "Find a postcode." The site will come back with one or more exact addresses with postcodes. Copy the postcode of the business in question.
Type http://www.2010.voa.gov.uk into your internet browser and hit Enter. Click on the "Find My Property Valuation" button. Check that the button next to "Postcode" is selected, and enter the postcode from step 2 into the box, then click "Search."
Choose the correct business from the list of addresses given. The rateable value for that business is in the second column from the right.