He said: "The patient or resident is the weakest voice in the system. It is a classic market failure - the user doesn't know nearly as much as the professionals, even with the internet."
Mr Prior said it was unlikely the CQC could give a "cast-iron guarantee" that it would be able to prevent future healthcare scandals such as Mid Staffs.
He also criticised a decision by the previous government to allow family doctors to opt out of out-of-hours care, saying the decision had let patients down.