Answer
The service works on the basis of a closed system which only includes the ISP and Phorm. No browsing or interest data leaves the ISP network and no personal user information is stored by Phorm's technology or shared with any party, including the ISP. Further, no browsing or interest data is passed by Phorm to advertisers or any other party.
As the system works on unidentifiable data the service can't know who you are or where you've browsed. Plus users choose - they opt-in via an unmissable online invitation, which means that the service is only activated after a person has explicitly decided to use it.