Holidaymakers complained to Thomas Cook about conditions at an all-inclusive hotel in Egypt before two Britons suddenly died there last week, but say they were assured nothing was wrong.

Alison Cope from Birmingham said she raised multiple complaints including about being served raw meat and drinks from unwashed glasses prior to the deaths last Tuesday of John Cooper, 69, and his wife Susan, 63, at the Steigenberger Aqua Magic hotel in Hurghada, which is on the Red Sea.

Five people in Cope’s party were among 13 guests who reported illnesses in the last week. Some suffered such uncontrollable diarrhoea that people defecated in the swimming pool on three separate occasions in the last fortnight, Cope told the Guardian. She said the hotel was unable to prevent other guests from jumping in unaware that the pools had yet to be disinfected.

One member of her party suffered headaches, breathing difficulties and fluid on the lungs, which a British doctor has since said appear consistent with Legionnaire’s disease, a lung condition that can be carried by contaminated water in air conditioning units.

Thomas Cook and the German hotel company Steigenberger said they were carrying out urgent investigations into food and water supplies as well as air conditioning systems after several guests reported stomach and breathing problems.

Facebook Twitter Pinterest John and Susan Cooper. Photograph: Blue Sky hotel/Facebook

The Coopers’ daughter, Kelly Ormerod, said on Sunday she believed “there was something in that room that’s actually killed them” and they may have inhaled something that poisoned them.

When they went back to their room after dinner there was a funny smell that they covered up with perfume, Ormerod told the BBC. The next morning they didn’t come down for breakfast and she found them “extremely ill” in their room. They had not been suffering from upset stomachs. Susan Cooper worked for Thomas Cook as a travel agent in Burnley.

The Red Sea governorate said an initial examination suggested John Cooper suffered acute circulatory collapse and sudden cardiac arrest. His wife was later rushed to hospital after fainting and underwent resuscitation attempts for 30 minutes but died.

An inspection of their hotel room found no toxic gas emissions or leaks, the prosecutor’s office said, but investigators for Thomas Cook have so far been denied access to carry out their own tests in the room. The travel firm said there was no evidence of carbon monoxide poisoning from its tests in other parts of the hotel.

Steigenberger said it had been told by the office of Egypt’s attorney general that a committee of experts “checked all equipment and devices in the room and in specific the air conditioners and cooling devices” and “reported that no trace of abnormal leaks, no poisoning or harmful gas leakage”.

More than half of the 301 Thomas Cook customers at the resort have been flown home but several remain ill.

Cope said fish and chicken served in the restaurants was “totally undercooked”, apparently because the hotel could not keep up with demand.

“I would get a drink of water and sometimes the water would taste chemical,” she said. “Other times you would be handed a glass which had been swilled rather than washed. When we asked what they were doing, they said that if they were really dirty they would put them in the dishwasher for 30 seconds.

“There was a barbecue on the beach and another guest bit into the chicken and it was raw in the middle.”

Cope said that after members of her family fell ill a few days into their holiday she complained to the Thomas Cook hotel representative but says she was told: “There’s no problem and no one else has a problem:” She escalated her complaint and was met by a hotel manager and a more senior Thomas Cook representative and “they dismissed what I was saying”.

Thomas Cook confirmed Cope had complained but neither it nor Steigenberger would comment on her claims.

“We are aware that a number of customers have come forward to say they have experienced illness,” a Thomas Cook spokeswoman said. “We are very sorry for any customers whose holidays have been spoiled.

“We take all illness very seriously and have taken the decision to expand our ongoing investigation into the sudden deaths of two of our customers at the Steigenberger earlier this week to include any other customer reports of illness at the hotel this summer.”

Steigenberger said the hotel was operated by a franchisee and that it had launched its own investigation into standards. The German company said it was “deeply saddened” by the deaths.

“We are really looking carefully to check the facts,” said Sven Hirschler, director of corporate communications.