From the terms & conditions here: https://giffgaff.com/gameplan/free_credit_report/application/#/terms
In these Terms and Conditions, "we", "us" and "our" refers to giffgaff,
Your credit score will be used by giffgaff to identify product offers that may be appropriate for your circumstances (however, this does not guarantee that there will be appropriate product offers available to you). You will then have the opportunity to apply for the product via https://giffgaff.com/gameplan/compare. It is important to note that there may be other products available from lenders who are not represented by this service. We receive a payment if you choose to take out a product, but this does not influence the suggestions we provide to you.
To provide the Services to you, we need to obtain your credit report information held in Callcredit’s credit reference database. By applying for the Services you agree that we can use your credit report and personal data information in this way.
By agreeing to receive these Services, you also agree to the information described in Clause 10.1 being used by us, the other parties identified in Clause 10.1, and selected third parties for marketing purposes including amongst other things to identify and offer you further products, services and offers which we think might interest you.
Which is rather odd, because all Clause 10.1 says is:
10.1 If you have any questions in connection with the Services, please contact us. You can contact us by email at http://www.callcredit.co.uk/contact-us/consumer-enquiries