Avon is the leader of a criminal gang which is well-known to use violence. He told his son, Bart, (aged 19) to attack a rival gang member, Viv.  He threatened to break Bart's legs if he did not do so. Bart, terrified, agreed and attacked Viv, inflicting serious injuries. 

On his way home, Bart saw Omar standing in the shadows at the side of the road.  Bart mistakenly thought that Omar was a member of Viv's gang who was about to attack him.  In fact, Omar was not a member of any gang and was waiting for a bus.  Bart stabbed Omar and inflicted serious injuries. 

 

Discuss Bart's criminal liability, focusing specifically on whether he could rely on any defences