I don't know how the new law reads (and doesn't really apply to me since I'm not in the UK anyway).
That said,
I think if you have a reactive dog you still have a responsibility to do your best to keep your dog from harming another dog.
Bates is not reactive, but he has no problem correcting rude behavior, and if the dog objects to a fair correction, Bates has no problem upping the ante and making sure his point is made. IOW, if your dog jumps on my dog's head uninvited it may very well lead to my dog poking a few holes in yours.
I see it as MY responsibility to prevent my dog from poking holes in other dogs no matter how warranted that hole-poking may be. This is in part why I have put far more in to training with Bates than with other dogs, because with a dog like him, I need him to be able to listen and defer to me even in high arousal/excitement situations.
Ideally, he does not get in to those situations to begin with, so to that end, owners of uncontrolled dogs may find *me* aggressing against their dog to keep him away from mine