Hi, I just googled this http://theindependentgeneralpractice...formation.html
The IGP is designed to compliment your NHS service, not replace it. With the patient’s consent we regularly update NHS GP's with relevant information about patient care. However, should a patient not wish us to share information with their NHS GP, we will respect those wishes.

So, it looks like they don't have to consult your NHS GP if you don't want them to, which I was quite surprised about. They would still need to adhere to the legal side of things (eg. mental health act, mental capacity act etc), for anyone who falls under that.