AN experienced deep sea diver who died during an expedition in Scotland had an epileptic fit, an inquest heard.

Hilary Lyon, aged 39, was exploring a wreck with Bolton Sub-Aqua Club when she got into difficulties on July 15, 2004.

Bolton Coroners Court heard that Miss Lyon, who lived in Water Street, Egerton, had been diving for 14 years when the accident happened.

Details of the dive were obtained from computers which divers carry with them.

They revealed that, for some unknown reason, she changed her gas cylinder too soon when she was on her ascent to the surface.

Experts believe that this caused the oxygen level to be too high, triggering a seizure.

She had bitten her tongue, which is consistent with an epileptic type fit.

The surface marker, which divers send to the surface to follow their way, was never recovered.

Miss Lyon, a mother of teenage boy, did not have a history of suffering from epilepsy or any other illnesses.

Dr James Francis, who is an expert in marine medicine, said: "When this happened she would have lost control and consciousness very quickly.

"There are different levels of tolerance for oxygen toxicity, and it varies not only from person to person, but can be different in the same person.

"So what she may have got away with one day could be fatal on another.

"Sadly this is quite common and there are about six fatal cases of this a year in the UK."

Coroner Jennifer Leeming recorded a verdict of accidental death.

She said: "Hopefully people who still dive will be able to learn from this as what may be safe today may not be tomorrow."

Miss Lyon's brother-in-law, Dr Mark Hall, said after the verdict: "This has highlighted that diving can be a dangerous sport.

"We are happy with the verdict and the family knows that she died doing something that she loved."