Concerns have been raised over the safety of firefighters who suffered suspected carbon monoxide poisoning while working out of a fire service vehicle.

Three Leatherhead crew members went to hospital on Monday evening after working in a mobile Incident Command Unit in Chertsey where flooding has caused evacuations and chaos.

It is understood that the on-board carbon monoxide alarm sounded “after the event” and excess carbon monoxide was found in the firefighters' bloodstream.

Seven-year-old boy Zane Gbangbola died in Chertsey on Saturday after he and his parents were taken ill at their flooded home.

Dave Herpe, chairman of the Surrey Fire Brigades Union (FBU), said he believed the firefighters had not been dealing with the flooding directly but had been working out of the mobile command vehicle at Chertsey fire station.

Mr Herpe said: "My understanding is that three firefighters have been to hospital and have been tested for carbon monoxide poisoning.

“We have safety concerns about the incident command unit that are yet to be addressed."

The £300,000 mobile command centre allows firefighters to co-ordinate their emergencies. But in June it was criticised as unfit for purpose by the FBU.

A Surrey Fire and Rescue spokeswoman said: "We would never put a vehicle into service if we had any safety concerns.

“We don’t know what the cause of the problem was so we cannot jump to conclusions."

She confirmed the firefighters had been working in the command unit and added: "They were not in there the whole time.

“They went out and about in the area. They were doing whatever was needed in the circumstances."

When asked about reports that more than three personnel had been affected, she said: "Certainly not to my knowledge."

On Tuesday the spokeswoman said in a statement that three firefighters had been checked out of hospital after feeling unwell following their shift.

She said: "We are pleased to say that they are now absolutely fine. An investigation into the incident is continuing, and as yet there is no confirmation of the cause or the origin."

Surrey Police have said the cause of Zane’s death is unknown and have not been drawn on suggestions that carbon monoxide could be to blame.