Hemlock is not the common species it once was, especially in farming areas like Galloway. It is as toxic to livestock as it is to humans, so farmers have all but eliminated it from inland areas. It is most commonly found coastally, having a preference for sandy soils, but that’s not to say it doesn’t lurk inland too. It is more common in E Scotland and S England.
It grows up to 2m tall, and has more delicate looking (fern-like) leaves and white flower umbels than many of its carrot family relatives. Cow parsely has very similar leaf structure . The key diagnostic of poison hemlock is its hairless, cylindrical, red spotted flowering stems. It also has an unpleasant mousy smell.
For a full rundown on how to distinguish poison hemlock from cow parsley, please see my post on cow parlsley.
Coniine is the main active toxin which attacks the central nervous system, leading to paralysis and subsequent asphyxiation. 8 – 10 leaves could send you to your maker, though there is much variation according to season, stage of growth, location etc. The toxins are more concentrated in the roots and seeds.
For more information on this and other members of the carrot family see “Know Your Carrots” and my in depth article – “An Introduction to the Apiaceae Family for Foragers”
For more discussion on toxic plants and fungi see “The Day I Ate a Deadly Plant: The Spectrum of Edibility”