An investigation into how 10 schoolchildren ended up in hospital after a swimming lesson has revealed that chlorine levels in Winsford Lifestyle Centre’s pool were ‘higher than normal’.

Health and safety officers from Cheshire West and Chester Council (CWaC) and pool contractors from the authority spent hours looking into the cause of Tuesday’s incident, in which the pupils and one teacher from Winsford High Street Primary School had to be taken to Crewe’s Leighton Hospital with minor respiratory symptoms.

Around 56 children had been at the centre, which is run by Brio Leisure, for swimming lessons, and it is believed most were poolside when some of the group in the water began coughing.

All three emergency services were called to the scene and the building was inspected thoroughly by Cheshire Fire and Rescue Service while the children were taken to a nearby rest centre set up by CWaC.

Evidence from the investigation, which was launched immediately, showed that the balance tank water combined chlorine level in the pool had been higher than normal and this could have caused odour and discomfort, which a CWaC spokesperson said was down to a ‘technical issue’.

“Low suction in the balance tanks may have caused a build-up of the higher level of combined chlorine and subsequent odour in the pool hall environment, which was caused by a technical issue with the suction in the balance tank and this will be rectified by an engineer.

“As a precaution, the balance tanks have now been drained and refilled with fresh water,” the spokesperson added.

Half of the 10 children taken to hospital were back in school on Wednesday while others recuperated at home; and the two pools at Winsford Lifestyle Centre were open as normal the following morning.

Cllr Mark Stocks , executive member for children and families, said in a statement: “The reaction of everyone at Winsford High Street Primary – both teachers and parents – to yesterday’s incident was first class – a credit to the school.”