A simple statement along the following lines will suffice:-
"Any information you provide to us will be regarded as confidential, and will not be disclosed to a third party for any reason without your prior consent. Your information will be stored securely, and used solely for the purpose for which it was provided. We will not send you unsolicited marketing information of any kind, or contact you by phone, post, or email unless you have indicated your consent.
You may request that your information is deleted from our records at any time by emailing (supply address)."