Monkshood

This is a highly toxic and poisonous plant that can be found throughout the UK.

It was the poison of choice in the book of the same name by Ellis Peters. The crime, the murder of Gervase Bonel, was, of course, solved by Brother Cadfael.

It's such a shame that such an attractive flower should be so poisonous to humans. The nectar-rich flowers attract a range of pollinators.