the law says that your dog must be under control when in public. Clearly allowing the dog to bite someone isn't having it under control. Therefore in law you and your dog are in the worng (well you really, not the poor dog)
I suppose the outcome will hinge on how badly the woman was bitten (if for example she had to have treatment for the bite, the medical staff may encourage her to contact the police) If it was just a nip, she probably wont do anything, but who knows. One thing for sure is to learn a lesson from this by always complying with the law and having your dog under control. If he had bitten a toddler who wandered too close to him, you could have been looking at a far far worse situation and if a child is permanently harmed or scarred for life by your dog, it's a bit lame to say "well you shouldn't have gone near him"