Kathy...only just read this...sorry youve had such a long wait for a reply!
almost all wildlife poisoning - placing of meat or egg baits in the open - is done by gamekeepers....until the 1981 Act came in many farmers and shepherds indulged in this practice too...even though its been illegal in England since 1911!!
anyway , the commonest chemicals to use have been pesticides which were being used to kill rodents [alphachloralose...now very difficult to obtain but still smuggled in from Ireland and Continent] or insects [carbamates such as carbofuran and aldicarb being the most common now]. These are all banned substances now...but the history of poisoning is such that some new thing will come along.
the people doing this now are trying to kill birds of prey, foxes, crows etc...but really, they dont care what they kill...if they can gey away with it...
when a kite gets killed it gets embarrassing....
its all disgusting and its all illegal..
hope that helps?