I reported the incident to the police. As (we all) thought, there was nothing to be done in my case, but at least the local beat officer is now aware of a potential problem. It appears it could have been influenced by a film called TV Weather Man, or something, with Nicolas Cage, where people throw fast food and drink at him in the street for apparently no reason. Nice.
I will not let this put me off walking, though a few years ago, I would have been devastated. Thank you for all your support and encouragement, it is much appreciated and gives strength.