Man who butted the passenger on C2C line is a met policeman.
- Commuter who stepped in to headbutt man 'threatening to stab people' on a packed train is revealed as an off-duty policeman
- Video of a man striking a bearded man on a c2c service was released on Thursday
- Commuters cheered and praised him for protecting passengers in East London
- Bearded man was allegedly harassing others and was restrained until Upminster
- Police then arrested him on suspicion of carrying a knife and a theft offence