Aconite is an innocuous blue or yellow flowered plant with dark green leaves, found in shady spots in many suburban gardens all over the world - but the roots of several species harbour a deadly toxin.

The lethal component is an alkaloid substance known as aconitine, found in particularly high concentrations in Aconitum ferox, Aconitum Napellus and Aconitum Palmatum.

The dark-coloured, tapering roots are occasionally mistaken for horseradish. A light touch of the juice causes a numb, tingling sensation - any more has a similar effect to cyanide, paralysing the breathing and stopping the heart.

In the Himalayas aconite is widely known as the source of a deadly nerve poison known as bikh, or nabee, which has been linked to the assassinations of several public figures.

Omar Asghar Khan, 48, the former Pakistan environment and rural affairs minister who was found hanging from a ceiling fan in 2002, is believed to have been a victim, as is Hussein Shaheed Suhrawardy, a former Prime Minister found dead in a hotel room in 1963.

The lethal properties of aconite have captured the imagination over the centuries. Also known as wolfsbane, in the Middle Ages the touch or taste of aconite was rumoured to turn human beings into werewolves, or alternatively to keep werewolves at bay.

It gained literary notoriety in Oscar Wilde's 1891 story Lord Arthur Savile's Crime, and more recently the children's author JK Rowling immortalised it in her Harry Potter books.

The boy wizard is taught that it is a wolfsbane potion that prevents his teacher Professor Lupin from turning into a werewolf at the full moon.

"What's the difference, Potter, between monkshood and wolfbane?" snaps Professor Snape, the potions master, in the first book of the Potter series.

When Harry says he doesn't know, Snape retorts: "They are the same plant, which goes by the name of aconite."

Aconite has also been known as leopard's bane, women's bane, Devil's helmet and blue rocket. It was allegedly used as an ingredient in witches' magic potions.

It has also had more practical uses, as a curare to smear on the tips of arrows for hunting. The Ainus tribe in Japan used a species of aconite to hunt bear, while the Minaro in Ladakh still use it to bring down ibex.

The Chinese used aconite poisons for both hunting and warfare.