The death cap mushroom can be found throughout the UK, closely resembles other mushrooms that are edible, and half a cap will kill you. The toxin is very stable, so won't be destroyed by cooking, and can't be easily cleared by the body - symptoms come on after several hours by which time it is too late, your kidneys and liver are done.
In Finland they eat the false Morrel which is poisonous ,they boil it in three changes of water and many have liver failure or die each year and still they serve it in top restaurants .