Cafés in Warner Bros Studios were closed last week after “foreign objects” were found in food.
A worker told The Sun a shard of glass was found in a half-eaten muffin left by a customer on Wednesday, July 17 at the studio in Leavesden.
Upon further investigation by bosses, 13 muffins contained metal pins forcing them to shut all of its four cafés at the attraction.
Warner Bros say the contaminated food was discovered before it left the kitchen before the studio tour opened and no food was served to customers.
A spokesperson said: “We are taking this matter extremely seriously; the safety of our visitors is our primary concern. We are working with the police to investigate the incident.
“No contaminated food left the kitchen and additional safe-guarding measures have been put in place as a precaution.”
Hertfordshire Constabulary opened an investigation into safety breach.
A spokesperson said: “We are investigating an incident at Warner Bros. Studios in Leavesden on Wednesday July 17 where foreign objects were reportedly found in a small amount of food.
“The food in question was intercepted before it was made available for consumption.
“Enquiries are continuing, and officers are working closely with the studios who are fully supportive of the investigation.
“If you have any information you believe could be useful to the investigation, please contact police quoting reference 41/65007/19.”
You can report information online at herts.police.uk/report, speak to an operator in our force communications room via online web chat here or call our non-emergency number 101.
Alternatively you can remain anonymous by calling Crimestoppers on 0800 555 111 or reporting information on their website at crimestoppers-uk.org