One very simple solutions to this issue is the Telephone Preference Service (TPS)
The Telephone Preference Service (TPS) helps if you want to make sure your telephone number is no longer available to businesses who do telemarketing and other “special” offers you may not want to receive. If you are receiving unsolicited sales (or cold calls), marketing voice recorded messages down your telephone line, and you have not given prior consent to receive such messages, you can ask the marketer to stop sending these. They are legally obliged to act upon your request.
To register for the Telephone Preference Service click on the link below. It costs nothing, but five minutes of your time (and up to 28 days to take effect), but it does help.
Failing the above (after 28 days), if you are still receiving such calls you can complain to the Information Commissioners Office.