Armed police swooped on a Halloween event after a passer-by saw people being bundled into the back of a van by men holding guns and wearing balaclavas.
But the group of 20 men and women were actually participants in a "physical horror" survival event called Outbreak which was taking place in the village of Albourne, West Sussex, on Sunday, organisers said.
Outbreak spokesman David Parker said: "Most of the participants thought the police were part of the event.
"It took a while for them to believe that the officers were actually from a real police force.
Halloween event sparks police alert - BT