A gas boiler that leaked carbon monoxide into a holiday bungalow and killed two children was the worst installation an expert had seen in 50 years, a court heard today.


Christianne Shepherd, seven, and her six-year-old brother Robert, from Wakefield, West Yorkshire, died after being overcome by fumes while on a family holiday in Corfu, Greece, in October 2006.


Their father, Neil Shepherd, and his partner, Ruth Beatson, both fell into a coma and were admitted to hospital, but survived the poisoning.


Richard Carson and Nicola Gibson, who worked for Thomas Cook when the incident occurred, appeared in Corfu Town courthouse to face charges of manslaughter and negligence.


They are accused of causing manslaughter by negligence in relation to the children, and of causing bodily injury by negligence to Mr Shepherd and Ms Beatson.


Nine Greeks, including staff from the Louis Corcyra Beach Hotel, are also due to be tried.


Harry Rogers, a retired mechanical engineer, investigated the bungalow at the Louis Corcyra Beach Hotel in Gouvia just after the tragedy.


He told the court the leak was caused by a catalogue of failings in installation and maintenance and said of work carried out on the boiler: “It’s the worst installation I’ve ever witnessed in 50 years.”


When asked why it had only just caused such problems after its installation nine years before, Mr Rogers replied: “(It’s) damn lucky.


“You can play with a gun for so long and it not go off but in certain circumstances someone can get killed.”


He described how a wired-out gas valve, a bypassed thermostat, the lack of a flue and chimney, and a gap between the family’s bungalow and the outhouse where the boiler was contained caused the leak of the poisonous gas.


Gaps in unfinished air conditioning pipes also contributed to the tragedy.


Mr Rogers said parts that should have been fitted were left on the floor next to the boiler and added: “The mistakes that were made were negligent and incompetent.”


He was also asked by the court what responsibility he thought Thomas Cook had in terms of maintaining the appliance.


“I don’t know how the tour operator operates,” he said, “but if any reasonable person that had any reasonable knowledge that could inspect that boiler – they did not need to be a rocket scientist to know something was wrong.”


Mr Rogers told the court a safety expert at the resort told him none of the bungalows had flues fitted.