From 1st July 2015, the way calls are billed is changing, and unless your number is a standard landline (01, 02), an 03 number or a UK mobile (07) these changes are going to affect your business.
All service charged numbers will be spit into 2 costs; the ACCESS CHARGE which is set by the phone company (contact them to confirm this charge) and the SERVICE CHARGE which the company being called (you) decides on.
Both charges must be made clear to customers and so it is important you review all your websites, business cards etc. to ensure you are in keeping with the law.
The changes are explained more fully here