Hemlock and Hemlock Water Dropwort

Hemlock Water Dropwort (Oenanthe Crocata)

Hemlock water dropwort is an extremely poisonous, perennial plant. It forms elongated root tubers and has erect, hollow, grooved stems. Leaves are pinnate and flowerheads of white umbels, 5-10cm across, are borne in July and August.

View more information on the RHS (Royal Horticulture Society) Oenanthe crocata and hemlock water dropwort webpage

Hemlock (Conium Maculatum) 

A poisonous plant, hemlock has a repellent smell when its leaves are crushed, helping to ensure that accidental poisonings don't occur very often - even livestock studiously avoid it. 
This biennial plant prefers damp places and can grow in huge colonies on waste ground, riverbanks and ditches, but can also be seen along roadside verges. It produces umbels (umbrella-like clusters) of white flowers in June and July.

View more information on The Wildlife Trusts Hemlock webpage

Another useful website is wildflowerfinder.org.uk