There are a number of regulations that apply to businesses that promote themselves using telephone and fax.
The Privacy and Electronic Communications Regulations 2003 govern direct marketing by telephone and fax.
The regulations also cover the Telephone Preference Service (TPS) and the Fax Preference Service (FPS). These are registers of individuals and businesses who have indicated that they don't want to receive unsolicited phone calls or faxes.
You must respect the wishes of any subscriber who asks you not to contact them on a particular phone or fax number, whether or not they are registered with the TPS or FPS.