[werdnal]

There is a type of rat poison that is harmless to other mammals and birds. Its a type of fibre pellet that the rats/mice ingest and it gums up their intestines, leading to lethargy and eventually they lapse into a coma and die. It claims to be more humane than anti-coagulant poisoning and works better as there is no resistant build-up as with some chemical baits. Not sure if I can post a brand name, but a search on Google containing the words "natural" "rat" and "killer" brings up a few references.

It is expensive though, and takes a while to be effective. I would doubt that the council rat man is forking out for that, but if the bait you can see is a pale pellet type, then perhaps your council is more well off than ours!