Ignoring it is an option I suppose. But I can see that if your dog goes AWOL and is picked up by the council or handed in as a stray to the council, that might cause you problems. I suppose if it's an elderly dog, that might not arise, but on the basis that if you break the law for long enough, eventually you'll come a cropper.
Whatever next? A dog licence for 38 1/2p or whatever it was?