A train company claims it is a "complete mystery" how an unconscious woman came to be left on a train parked in sidings.

Sue Kelly, 33, spent four hours in the carriage of the Great Eastern train after she fell into a diabetic coma on her journey home from work.

For the first two hours she was in a deep coma, then awoke to find she could not get out as the train doors were locked.

It was only when the train was moved into Southend Victoria station for cleaning that Miss Kelly, of Oak Walk, Leigh, was able to disembark.

Peter Northfield, spokesman for Great Eastern, said that the trains drivers usually walk through all the carriages before leaving the train in sidings.

He said: "It is a complete mystery how Miss Kelly was missed.

"We are reviewing our procedures for parking trains in sidings as a result of this incident.

"This was a busy rush hour train yet none of 1,000 passengers appears to have noticed Miss Kelly.

"Barely a day goes by when someone is not taken ill either on our trains or on the stations and an ambulance needs to be called. Nine times out of ten it is another passenger who alerts us or the emergency services."

Miss Kelly, who works for an accountants in London, has been a diabetic for 20 years. This was only her third - yet her most severe - coma.

She said: "I was feeling fine one minute then the next thing I knew I woke up and the train had stopped and was empty. I did not where I was or what the time was. It was very distressing."

Simon O'Neill, head of diabetic care service at the British Diabetic Association, said: "It is very concerning that a woman should be left on a train like this.

"What happened to Miss Kelly is what we would expect to happen - she came out of the coma herself after a couple of hours.

"Diabetics fall into a coma either because their sugar level is too high or too low. People who know the sufferer and see them become drowsy should offer them some food.

"However, anyone who finds a person unconscious should call an ambulance straight away."

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