Metal detectorists attending the Coil to the Soil rally in Yorkshire had anticipated a gentle four days scanning 400 acres of land for treasure.

But the event descended into chaos when a birthday cake laced with cannabis oil was unwittingly handed around, causing several attendees, including a 69-year-old church organist, to “drop like flies” while others burst into song or started dancing.

A fleet of eight ambulances was sent to the scene, as well as a rapid response vehicle, two doctors, two clinical supervisors and a Hazardous Area Response Team, trained to respond to serious public health threats

At last 13 people were rushed to hospital - many so unused to taking drugs they feared they were suffering a heart attack or even dying.

A 48-year-old woman from Co Durham was arrested on suspicion of supplying a class B drug and has been bailed while inquiries continue, South Yorkshire Police said.

The havoc began when Gary Cook, a keen metal detectorist who is well known in such circles, strolled around the site in the village of High Melton near Doncaster at around 5.30pm on Saturday, offering guests a slice of chocolate cake baked by a female friend to celebrate his 50th birthday.