Plants such as the opium poppy and strychnine tree are being grown in a corner of Alnwick Garden, Northumbria – Hogwart's in the Harry Potter films – to warn youngsters about the dangers of drug taking. Local schools will be offered free guided tours of the gardens, which were developed by Jane Percy, Duchess of Northumberland, as part of a drugs awareness programme.

"I thought if you can engage a child through stories of gruesome and very painful deaths, which is how most of these plants kill, you can then teach them about other things by stealth without them realising they are being taught a valuable lesson.

"If they knew that, it would also fail," the duchess told Sky News. "It was all about storytelling and there are so many great true stories out there which have been forgotten really."

Mark Fox, a local teacher said the guided drugs tour would be of enormous benefit: "These students will take this information back to school, to their friends and to their families. It is a marvellous opportunity to be able to come here and to learn about the dangers of drugs in a garden where they are being grown."

Risky gardening

According to the Alnwick Garden website, gardeners who work here treat the plants with the utmost respect, wearing gloves when working with them. The warning on the gates starkly states: "These Plants May Kill".

There are over 100 deadly plants of varying deadliness grown in the Poison Garden, including Nux vomica (a form of strychnine), hemlock, which the Greek philosopher Socrates used to commit suicide, and the opium poppy, which is used to heroin.

There is also the plant Ricinus communis – the castor oil plant. A single seed from this plant can kill, causing nausea, severe vomiting, convulsions and subsequent disintegration of the kidneys, liver and spleen.

In 2014, there were 3,346 drug poisoning deaths registered in England and Wales, the highest since comparable records began in 1993, according to the Office for National Statistics. Of these, 2,248 (or 67%) were drug misuse deaths involving illegal drugs. The mortality rate from drug misuse was the highest ever recorded at 39.9 deaths per million population.