Botanist and food presenter James Wong tweeted a picture appearing to show bunches of the toxic flower next to spring onions in a seasonal produce display titled "eat well".

If consumed, daffodils can cause symptoms including vomiting and diarrhoea.

Mr Wong wrote that daffodils can cause "plant-based poisoning" if the bulb is confused with members of the onion family, adding that staff needed better training.

He wrote: "Daffodils are the single most common cause of plant-based poisoning as people mistake their bulbs (even cut flower buds) for crops in the onion family.

"@marksandspencer I don't want to get any staff in trouble. But you need better training asap.

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"Daffodils are filled with microscopic crystals, so biting into one is like swallowing a box of tiny needles. Properly nasty."

If eaten, daffodils can cause vomiting and diarrhoea and irritation to the mouth and throat, according to the British Columbia Drug and Poison Information Centre, which said symptoms can last anywhere from four to 24 hours.

M&S apologised for any confusion.

"Customer safety is our priority and our British daffodils are clearly labelled with an on-pack warning that they are not safe to consume," a spokesperson said.

"This was a genuine error in one of our stores and as a precaution, we are reminding all stores to make sure the flowers are displayed properly."

In 2015, Public Health England (PHE) wrote to supermarkets warning them of the dangers of displaying daffodils near food to prevent customers from eating the poisonous plants by mistake.

PHE said people had been known to mistake daffodil bulbs for onions and the stems of a popular Chinese vegetable.