CAP393
Fatigue of crew – responsibilities of crew
146 (1) A person must not act as a member of the crew of an aircraft to which this article applies if they know or suspect that they are suffering from or, having regard to the circumstances of the flight to be undertaken, are likely to suffer from, such fatigue as may endanger the safety of the aircraft or of its occupants.
So as soon as fatigue is reported then the reporter is surely danmed having commited a criminal offence. Not very encouraging for honest reporting is it?