The mother of two children who died from carbon monoxide poisoning in a Greek hotel has said she holds the tour firm "totally and utterly responsible".
A faulty boiler has been blamed for the children's' deaths
Sharon Wood told BBC One's Panorama programme that Thomas Cook should have made better safety checks on holiday bungalows at the Corcyra Hotel, Corfu.
But the company, whose tour rep carried out a tick-box survey of the hotel, said it had followed industry rules.
Christi and Bobby Shepherd, from Horbury, West Yorks, died in October.
The seven-year-old girl and six-year-old boy were on holiday with their father Neil Shepherd and his partner Ruth Beatson when all four where overcome by carbon monoxide fumes.
The gas had leaked into the room from a boiler, through holes drilled for an air conditioning unit which were not sealed properly.
Mrs Wood said: "I hold Thomas Cook totally and utterly responsible - they should have checked the place they were sending their clients to was safe.
"You do expect when you book through a British tour operator that things are going to be done to a similar standard we have in Britain."
In a statement, Thomas Cook said it had complied with guidelines issued by the Federation of Tour Operators (FTO).
FTO rules state gas appliances used in living accommodation have to be serviced annually and checked by a UK gas safety engineer.
Sharon Wood said the firm should have carried out better checks
But the FTO told Panorama that because the gas boiler was not technically inside the accommodation it did not have to be checked.
Thomas Cook said at least two other tour operators also carried out a safety audit which failed to identify problems with the boiler.
The firm said it was "shocked and saddened" by the deaths of the two children.
"Never before in the company's 165-year history has it experienced a situation more tragic and again wishes to express its sincerest condolences to the family and friends of the children."
But the company said it could not comment any further on the case because an investigation into the deaths was still going on.
"The company is determined to do everything in its power to ensure that there is no similar case in the future," the statement added.
Mrs Wood hired an engineer, Harry Rogers, to inspect the safety of the bungalows.
He said he found a catalogue of faults, including a thermostat, designed to shut down if hot gases were detected, which had been rewired to override so it did not work properly.
"In my opinion first and foremost the contractor or whoever installed them acted negligently," said Mr Rogers.
The authorities in Corfu are still considering whether to bring manslaughter charges against hotel's owners, hotel workers and the bosses of the companies which installed the boiler.