Hundreds of birds of prey are deliberately killed each year with poisons that have no legal use, according to MPs.
The Environmental Audit Committee says confusion over wildlife laws means criminals often escape unpunished.
It is particularly worried about carbofuran, a chemical used by rogue gamekeepers to kill raptors.
A Defra spokesman said it had banned possession of the chemical, but the MPs insist that it has not.
The chemical is devastatingly toxic to birds. A gamekeeper in Skibo, Scotland, convicted of poisoning birds in 2011, was found to have possessed 10kg of the chemical - enough to kill every raptor in the UK by breaking down its nervous system.
The committee learned that there had been 633 reported cases of poisoning of birds of prey, of which half involved carbofuran.