Shame on the GP
Looks like a clear breach of patient confidentiality to me.
Based on my experience in the emergency services:
* When a medical professional has concerns that a person may pose a risk to himself or to society, the person is referred to the social services, where professionals specifically trained to deal with these sort of situations follow up the case.
* A medical professional is obliged not to disclose information about a patient's condition without the latter's approval. Mere suspicion that a crime *may* have been committed, regardless of what the police would have you believe, is not a valid reason to breach that confidentiality.
This GP should have discussed the case with her team and a number of options could have been taken, without breaching professional and ethical standards, including as mentioned, referral to a psychologist or to the social services, patient counselling, etc.
I understand that the bloke may be annoying, a complete twat, etc., and someone of weak character may easily feel intimidated or overwhelmed, but shopping a patient to the police is just not what you do. Especially in this case where, given social hysteria surrounding sexual crimes, nobody is going to risk his career for this guy.