The company behind one of Ipswich’s best known leisure clubs has admitted risking the safety of its members after five people received hospital treatment following exposure to a noxious substance.

Following an Ipswich Borough Council prosecution David Lloyd Leisure Ltd pleaded guilty to contravening health and safety regulations at a plea hearing before the town’s crown court.

It admitted an offence of being an employer breaching it general duty to other than an employee. The charge relates to what is also known as Next Generation at The Havens in Ransomes Europark.

Sentencing has been adjourned until July 29.

David Lloyd Leisure Ltd, based in Hatfield, Hertfordshire, denied a second similar charge involving two members of staff.

Prosecutors have said it will not pursue the accusation and it has been left to lie on file.

The incident occurred at around 6.45am on February 22, 2012, while swimmers were using the fitness club’s pool.

Five people required hospital treatment for breathing difficulties, although six were initially mentioned in the charge, following exposure to chloramines.

One of the swimmers given medical treatment said he was put on a steroid nebuliser for three hours.

Speaking at the time the 70-year-old from Ipswich said: “I was swimming along and all of sudden there was a burst of liquid and I was enveloped in what I believed was a yellow cloud of chlorine.

“It was like breathing in fire. It left me feeling sick and breathing hard.”

He was put on a course of steroid treatment and said he was told he would need a lung capacity test three months later to ensure there is no lasting damage.

“It’s still early days but my lungs are bad at the moment,” he said.

Thirteen people had to leave the swimming pool area, including Wendy Turner, of Landseer Road, Ipswich, who said: “There was pure yellow liquid pouring into the pool from a pipe or a vent.

Shortly after the incident a spokeswoman for David Lloyd Leisure said: “We can confirm that three routine pool tests were carried out – two at 5am and one at 6am – prior to the club opening at 6.30am, which revealed that chlorine levels in the pool were well within the normal parameters.

“There were four first aiders in the vicinity at the time of the incident and we complied with our standard health and safety procedures.

“We take the health and safety of our members extremely seriously.”