Troops from the 7th Battalion Royal Electrical and Mechanical Engineers, became ill after working and sleeping in an aircraft hangar at an airfield in Hullavington, near Swindon.

Military officials have now ruled out carbon monoxide as the cause of illness in the 42 men and one woman.

A military environmental health team and two toxicology experts from Guy's Hospital in London have been carrying out tests on the troops.

Blood samples

They say that the fumes possibly came from an organic solvent or a cleaning product.

A spokeswoman said: "They have done a series of tests comparing carbon monoxide with the blood samples taken from the soldiers and they don't match up.

"They believe it may be something like cleaning fluids or aviation fuel and will be carrying out tests over the next couple of days to assess every possibility."

The troops were treated at Swindon's Princess Margaret hospital for suspected carbon monoxide poisoning, and 43 were kept in overnight.

A sergeant whose condition was described as "serious" earlier on Tuesday, is now stable. The company commander, a major, is also said to be among those affected.

An army spokeswoman said the troops were taken to hospital shortly after 2200GMT following complaints of headaches and nausea.

Cleaning agents are now being blamed

It is believed the soldiers, who were working on Lynx and Gazelle helicopters in shifts, had been using petrol generators to power tools in the hangar.

The incident could result in disciplinary proceedings.

"If, and only if, there was found to be some negligent or unreasonable care taken, there will no hesitation in taking the necessary action to make sure it doesn't happen again," the spokeswoman said.

The soldiers, who are based at Wattisham, Suffolk, were among 400 taking part in Operation Lightning Storm around the Gloucestershire/Wiltshire border to demonstrate helicopter support in battle conditions.

The Army said most of them were due to be released from hospital on Tuesday night, but 10 would be kept in under observation for a further 24 hours.