Therapists understand and completely respect the need for privacy and discretion when discussing sensitive issues. All psychotherapists and counsellors abide by stringent professional codes of ethics, set by their membership bodies, which include a commitment to the utmost confidentiality.
If what you share in your sessions seems to indicate a high risk of serious harm to yourself or someone else, then your therapist will most likely want to discuss that further with you, to see if anyone else might need to be informed. However, such a disclosure would wherever possible be made with your full involvement and consent.
For UK therapists, it is a professional requirement to have regular Clinical Supervision. This means that if you are undergoing current therapy, some details of the sessions may occasionally be discussed by your therapist with their clinical supervisor. Any such discussions are strictly bound by the same professional codes of confidentiality that apply to your own counselling sessions.
For clients under 18, there are certain limits to confidentiality in order to conform to the safeguards of UK Child Protection laws.