Posted: 22/04/2013 at 18:00
I'm not so sure. Unless you read gardening mags regularly, or chat with up-to-date gardeners, it's not exactly widely publicised that certain prodcuts are no longer legal to use. I meet all sorts of gardeners who don't know stuff has been banned and that old products have to be disposed of properly and not just poured away or dumped in the bin.
Unless relationships with this neighbour are bad, or he/she is know to be an idiot, a quiet word might go a long way and failingthat, a word with the environment office at the local council.