I'm not sure. I am the type to intervene and pre kids I stopped a fight on a London bus. I've done it recently to help an old woman who was being fleeced by some con artists. I somehow knew though I'd be in no danger and I was right. They walked off almost as soon as I approached them. The adrenalin was pumping and I made a right scene shouting after them. I'm not sure I would have done if it was a violent assault as I had my DCs with me. Those women in woolwich were incredible.
DH gets cross with me starring at people being shitty to their kids.
I would also worry my involvement would mean I'd put Nigella in a worse situation though l can see myself calling 999 to report an assault.