Exclusive: Cigarette theory over fire tragedy

But investigators have also said they cannot rule out the possibility the fire was started deliberately.

William Beal, nine, Anthony Hudson, also known as "AJ", five, and their three-year-old sister, Maddie Hudson, died when a ferocious blaze tore through their home in Clarence Avenue, Bridlington, on November 11.

Their mother, Samantha Hudson, 27, who was seriously hurt and remains in a stable condition in hospital, still does not know they are dead.

Steve Henry, specialist fire investigation officer at Humberside Fire and Rescue Service, said: "At the back of my mind there is always the thought that somebody could have introduced that naked flame in there.

"I can't totally rule it out 100 per cent and that's why I will mention it in my report, but to me and the team the most likely cause is a carelessly discarded cigarette."

A joint investigation by Humberside Police and Humberside Fire and Rescue Service has concluded the blaze was probably started when a cigarette that had not been fully extinguished fell onto clothing near the bay window in the ground-floor living room.

Mr Henry said the cigarette would have charred the material as its slowly buried itself. It can take 20 minutes or several hours for the smouldering material to produce a flame in such circumstances, Mr Henry said.

The family – who were in their bedrooms on the first and second floors of the three-storey, mid-terraced property when the fire broke out – appear to have been extremely unlucky as a flame is only produced in about 30 per cent of such cases, Mr Henry said. "It was a severe fire that started from a humble beginning," he added.

Smoking materials are believed to have been responsible for most of the 10 fire deaths in the brigade area last year.

Confirming the results of the investigation in a statement, a brigade spokeswoman said: "Fire investigators have been working with the police and forensics experts and it has now been confirmed that the most likely cause of the fire was due to a cigarette which had not been fully extinguished." The investigation was launched almost immediately, Mr Henry being made aware of the incident soon after a 999 call was made by a neighbour at 11.58pm.

He led the inquiry and was assisted by another specialist officer from the brigade and a police scene of crime officer.

They quickly established that the seat of the fire was in the living room, and within a fortnight police said the blaze appeared to have been a "tragic accident". The living room, which was gutted, was excavated by the investigators with some evidence being sent to a forensic science laboratory in Wetherby for analysis.

Mr Henry is now writing a report detailing his findings that will be submitted to the coroner. This will form part of an inquest into the children's deaths, which will seek to establish how exactly they died.

Ms Hudson is understood to have suffered severe smoke inhalation and has yet to regain consciousness.

Mr Henry said that although he had not been able to speak to her he had gathered witness statements from neighbours and a member of Miss Hudson's family who was babysitting for her that night.

"We know what time Samantha came home that night and who was in the house," he said.

"Although we haven't been able to talk to Samantha we were able to talk to the person who was babysitting for her."

Neighbours and the emergency services fought in vain to revive the children in the street after they were pulled from their home, one describing them as being "like little rag dolls". They died in Scarborough Hospital a short time later.

The children were buried three weeks later after an emotional funeral at Emmanuel Parish Church, less than half a mile from the scene of the tragedy.

Mother not told of child victims

AFTER being taken to hospital in a critical condition following the fire that killed her children, Samantha Hudson's condition has improved although she is still too unwell to be told about the tragedy.

The 27-year-old was stable yesterday but remains in hospital nearly two months after the fire.

Her parents, Robert and Sharon Hudson, have already revealed they are dreading the moment when they have to tell her that her children are dead.

They said in a statement: "We just do not know how we will cope, which one of our grandchildren to grieve for first. How do we carry on and move on from this in order to help our daughter?

"We are terrified how Sam will react and how she will come to terms with the devastating news."

The fire happened on the birthday of the couple's youngest daughter, Hayley. The family had visited the house hours earlier to celebrate.