The jury at the Coroner’s Court also urged people to think twice about what they throw onto fires, after hearing about the “freak” circumstances when a crisp wrapper thrown onto a dying coal fire blocked the chimney causing carbon monoxide to be released into the family sitting room.

The scene was described by coroner Dr Des Moran as one of the saddest he had ever come across.

The television and Christmas tree lights were still on when the bodies of 52-year-old Trevor Wallwork, his 12-year-old daughter Kimberley and his nine-year-old son Harry were discovered in the sitting room of their home.

The jury was told that a plastic bag from a crisp multipack was thrown onto a coal fire which was not hot enough to melt it, but filled it with gas “like a hot-air balloon”, so that it blew up and became lodged in the chimney, obstructing it.

Chief fire officer Paul Coyle who attended the scene said that death would have occurred within minutes given the high levels of carbon monoxide released. Mr Coyle pointed out the chimney flue had been recently cleaned and was in good condition.

When firefighters and police arrived at the scene they found Mr Wallwork sitting in an armchair facing the television with a blanket over his knees and his head slumped to one side. His two children were lying on the floor. All three were pronounce dead at the scene.

Mr Coyle told the jury that after climbing up on the roof he concluded that the chimney was obstructed and, using a tongs, removed the crisp bag which was 1.2m from the top.

Mr Coyle pointed out that the toxic carbon monoxide gases which were released could not be seen or smelt. He said carbon monoxide detectors should be installed in all homes using any kind of combustible fuel to prevent such a tragedy recurring.

Coroner Dr Moran was told that Mr Wallwork’s wife Susan, who was in Hospital being treated for cancer at the time of the tragedy, had died six months later.

Her daughter Vicky Barnes, who raised the alarm, said she hoped that lessons would be learned from the tragedy. Speaking after the inquest she supported calls for the installation of carbon monoxide alarms and said people should think about what they throw onto fires.