I haven't ever trained new physicians, but I've trained plenty of new psychologists, and some times doctors have really stupid ideas(just read through this site). Based on the information you have provided, I do think the doctor's actions are questionable, but I can still think of reasons this doctor could use to justify his actions. I know that you already said you are going to talk to your GP, which I think is the safest route for you to remain confidential and get good advice, but I also want to respond to some of the other advice you have been given.
1. Going to the police. The police will take your complaint, but there will be virtually NO confidentiality and the DA will be unlikely to do anything considering you wrote that he asked you, who I presume were a legal adult at the time, for permission. I believe DAs don't consider going after unethical actions unless they are also illegal. Because their is little to no confidentiality with the police, the chances of you be embarrassed and harassed, or the complaint being completely mishandled, goes up in my opinion.
2. Some have also suggesting suing the doctor, but this costs money and you have to have really solid ground to be successful. If he is a peeping tom, then he would not have recorded his actions and it would be a case of your word against his. If he had violated others, then you would have to find those people and that would be really hard to do.
3. One other suggestion was to go through the hospital ethics committee, which typically is a multidisciplinary team including a chaplain. The good side of this is that you can remain perfectly confidential and they will have likely have personally interacted with this doctor and thus have may some idea about his character. The bad side is that they likely know this doctor thus will be biased and they don't really control his ability to practice. This doctor can just quit and move away which saves the hospital embarrassment and so they may find the reasons to dismiss the complaint.
4. On the other hand, the state medical board that licenses this doctor has complete control over his license and will not be biased by a personal relationship. They have full authority granted by the state to conduct investigations when needed. Also, they have the most experience with handling complaints and thus will likely give you the best outcome--in my opinion. If they find this doctor in error, then legal action could be taken by you and you will have solid ground backed by the highest authority in the state. His malpractice insurance company would likely be knocking on your door to settle before being taken to court.