If you are asking this because of unwanted marketing calls you can register with the Telephone Preference Service.
If you have supplied your number at some time because you were a customer you can request that they remove your details or at least to desist from calling you.
I had this problem with my bank calling to "Discuss my Account". When I complained they said that I had supplied my number when opening my account. I reminded them that it was not an option not to and the number was for emergency use only.
Not sure of any legal requiremnt but I'm sure someone else might know.