Holiday giant Thomas Cook has been blamed for the deaths of two children during a family holiday in Corfu, Greece.
Neil Shepherd said his children Robert, six, and Christianne, seven, died from carbon monoxide poisoning from a faulty boiler because Thomas Cook failed to carry out checks.
Speaking at the inquest into their deaths at Wakefield Coroners Court, he said: "I firmly believe my children would be here today if Thomas Cook had carried out an inspection of those boilers."
Robert and Christianne died in 2006 while the family was staying in a chalet in a four-star resort. They were found dead by a cleaner, who also discovered Neil and his then-girlfriend, now wife, lying in comas from the deadly fumes.
Their mother Sharon Wood also stated Thomas Cook was responsible for the tragedy. She said: "I want to look further up the chain of command in Thomas Cook. I want to know why those gas boilers were not identified, why they were not serviced regularly.
"This is not just a difference of local standards abroad. This is gross negligence. Ultimately, my children paid the price with their lives."
An investigation found a faulty boiler in the chalet, which had not been repaired correctly, caused deadly carbon monoxide to leak in the air. Compounding the fault, a safety device had been short-circuited on purpose.
Coroner David Hinchliff said Shepherd was consumed by guilt and remorse at the deaths of the children while in his care. He had suffered mentally as a result of their loss, with memory problems and post-traumatic stress disorder. The inquest continues.