A hallucinogenic toadstool mushroom is growing in the gardens of Buckingham Palace.

The red and white spotted Amanita muscaria species - also known as fly agaric - has been discovered by Alan Titchmarsh while on tour of the grounds with ecology expert Professor Mick Crawley.

The discovery of the mushroom - which is likely to have grown on the 40-acre land without being specifically cultivated - was recorded during a 12-month study for ITV show The Queen's Garden, which is to be aired on Christmas Day.

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Mr Titchmarsh asks Professor Crawley if the fungi is edible, to which he replies: “That depends what you mean. It’s eaten in some cultures for its hallucinogenic effects. But it also makes people who eat it very sick.

“The old-fashioned thing to do was feed it to the village idiot, then drink his urine because you get all the high without any of the sickness.”

Mr Titchmarsh, known for presenting BBC gardening programme Ground Force and the annual RHS Chelsea Flower Show, then says: “I think I’ll forgo that and stick to some normal mushrooms”.

“Not something to try at home,” he added.

Chemicals muscimol and ibotenic acid found in the fungi cause psychoactive effects such as drowsiness, hallucinations, mood changes, euphoria and disassociation.

The plant has a long history of religious and shamanic use dating back around 10,000 years.

However, unlike psilocybin mushrooms - which were reclassified to Class A in 2006 and have been more popular for recreational use - the legal status of selling fly agaric in the UK remains complicated. Possession is not illegal.

The physical effects are described as "undesirable" and the chemicals can carry risks of poisoning and death, according to drug advice charity Talk to Frank.