The Medical Council Guide to Professional Conduct & Ethics state in paragraph 59;
Concerns about a colleague’s abuse of alcohol or drugs or other health problems
59.1 If you are concerned about a colleague’s health or professional competence due to the misuse of alcohol or drugs, a physical or psychological disorder or other factors, your primary duty is to protect patients. If there is a risk to patient safety, you must inform the relevant authority of your concerns without delay. If there is no current risk, you should support your colleague by advising them to seek expert professional help or to consider referral to the Medical Council’s Health Committee.