It's not illegal to feed
I just spoke to one of the caregivers who said that there is a man threatening to call the police when she feeds the cats. She gave him a Responsible Feeding brochure but he didn't bother and he claims there are ants going into his flat (how this is related to her feeding the cats downstairs, when she cleans up is beyond me). She said she had seen him attempt to kick the cats.
He stopped her this morning and said he'll call the police so she asked what to do. If someone does bother you, tell them that you WOULD like them to call the police so you can report them for bothering you. This is of course after you have tried explaining to them what you are doing, and they continually ignore you and harass you. Most people are reasonable, but some people will not listen to reason - in which case call their bluff. If you are feeding responsibly and feeding, then there is nothing to worry about. Feeding is NOT illegal as long as you clean up so don't be worried about the police. Just explain what you are doing and do it politely and calmly - this will be a good contrast especially if the complainant is yelling and screaming.