Baffled bosses at a school in Stevenage are scrambling to find out what caused three people to be taken to hospital yesterday (June 12), after tests showed "no evidence of carbon monoxide".

In a letter to parents, which has been seen by the Comet, the school has claimed that tests carried out on the three people taken to hospital show "no evidence of carbon monoxide", and they believe all three incidents are "unrelated".

The letter also says that a Gas Safe Registered heating engineer did not detect any of the potentially deadly gas inside the building, but an external health and safety inspection will take place.

"Today, the school was thoroughly tested and inspected by a Gas Safe Registered heating engineer, and carbon monoxide has not been detected in any area of the building," the letter reads. 

"The member of staff and two children who were taken to hospital have all now been discharged and medical tests have shown no evidence of carbon monoxide in their systems.

"All three incidents are now believed to be unrelated to each other."

Police, fire and ambulance crews were called to the Mildmay Road school just after 1pm, following reports of a number of children and adults becoming unwell.

One adult and two children were taken to Lister Hospital by ambulance with suspected carbon monoxide poisoning, while a further six adults and nine children were assessed at the scene.

Martins Wood also confirmed that the school will remain closed tomorrow (June 14), but plans are in place to reopen on Monday.

"Out of an abundance of caution, we will be keeping the school closed tomorrow for a further inspection by an independent specialist," the letter continues. 

"We have also been in contact with Hertfordshire County Council to request an external health and safety investigation.

"I would like to reassure you that we have carbon monoxide detectors at our school and these are fully operative.

"We hope to reopen the school on Monday and will keep you informed of any updates via email and social media."