As the parent of a vicious child - I will say that a child of almost 3 knows what he is doing. Only he doesn't know why.

Legally, if another child is getting hurt, it is your DUTY to restrain and remove (if possible) the offender. You can't let a bully's rights infringe another child's right to not be assaulted. You may have to check out local law, but I know that's UK law and Aus law is usually pretty similar.

My son has been a real rotter for two weeks now: Nursery told DH but he reckoned it was DS just being a bit boistrous. Now it's serious. Our nursery are talking about if he doesn't improve with the measures we are taking they will get a behavioural specialist in to see what else we can do.

Quite frankly, if it were my child being attacked all the time I'd be furious if all Nursery did was ask for a fake apology - which often wasn't given. I'd want that child picked up and removed from the area, which is what I've told Nursery to do and am giving them written permission as they're a bit jittery about that. Nursery have never blamed the victim (and I'd be cross if they did): if DS was being attacked then fair enough, but he's not. HE has the problem, not the person who "stood too close" or "thought about a certain toy" or whatever.