A snack “marketed to young children” has caused severe hallucinations and sickness, a school has claimed in an emergency warning to parents.

St Alban’s primary and nursery school in Holborn, central London, alleged that cereal bars called “Astrosnacks” had been offered to a pupil somewhere in London.

In a letter to families, interim headteacher Rebecca Harris said the Metropolitan Police had issued an alert about the food and claimed it was linked to “extremely violent bouts of sickness and severe hallucinations”.

However, while Scotland Yard said it had been “made aware of an incident involving a possibly fake snack bar”, it added: “No crime report has been made and the allegation has not been substantiated.

“Police have not been able to speak directly to the parties who were apparently affected.”