Obviously I have always intervened even before joining my current profession. I am proud that so many of you feel the same way that we must stand up for our fellow man. I would like to stress however that I would say that rather than get physically involved you can always (apart from on the tube) get on your mobile phone descreatly and call the police. Identifying yourself as a witness when the police arrive and tell them what you have witnessed. Instinct and red mist will kick in when we see some crimes but if they turn on you, step back, get some space and when able call the police. Dont get into a stand up fight.